RingCentral’s VoIP service isn’t the cheapest option right out of the box, but it does include features that other providers charge extra for (such as generous toll-free minutes and unlimited video conferencing). Plus, RingCentral offers price matching on plans with less than 50 lines, so you can rest easy knowing you’re getting the best possible price for your service.

That being said, Grasshopper doesn’t offer any conferencing tools. For that, you’ll have to sign up for join.me—Grasshopper’s sister company. This service offers both video and audioconferencing, but it does cost an extra $10–$30 per month. That’s another strike against Grasshopper, since most providers in Grasshopper’s price range include conferencing features.

While understanding the basics of VoIP and SIP is important, setting one of these systems up will require some general network knowledge, too. For the best quality, you will need to meet a minimum upstream and downstream data throughput requirement. In addition, you'll also need to meet a minimum latency number (that is, the time between when a signal leaves a remote computer and when your system receives it), typically measured in milliseconds. It is possible to test your network connection to see if it will support a VoIP service. RingCentral offers this service from their website, other vendors like to have their service engineers do it for you.  

GoToConnect VoIP is a simple setup if you buy their preconfigured phones—which come from recognized names like Cisco, VTech, and Panasonic, so quality isn’t an issue. GoToConnect’s customer service is US-based, with 24/7 phone, live chat, and email options, as well as specific lines for small businesses, larger businesses, government entities, and education clients. GoToConnect also hosts an exhaustive YouTube channel dedicated to understanding phone systems and features.

Private VoIP systems can be physical hardware PBX appliances, converged with other infrastructure, or they can be deployed as software applications. Generally the latter two options will be in the form of a separate virtualised appliance. However in some scenarios, these systems are deployed on bare metal infrastructure or IoT devices. With some solutions, such as 3CX, companies can attempt to blend the benefits of hosted and private on-premises systems by implementing their own private solution but within an external environment. Examples can include datacentre collocation services, public cloud, or private cloud locations.

In 1999, a discrete cosine transform (DCT) audio data compression algorithm called the modified discrete cosine transform (MDCT) was adopted for the Siren codec, used in the G.722.1 wideband audio coding standard.[74][75] The same year, the MDCT was adapted into the LD-MDCT speech coding algorithm, used for the AAC-LD format and intended for significantly improved audio quality in VoIP applications.[76] MDCT has since been widely used in VoIP applications, such as the G.729.1 wideband codec introduced in 2006,[77] Apple's Facetime (using AAC-LD) introduced in 2010,[78] the CELT codec introduced in 2011,[79] the Opus codec introduced in 2012,[80] and WhatsApp's voice calling feature introduced in 2015.[81]
Fortunately, there are several dedicated residential VoIP providers who offer nationwide service, usually with worldwide calling plans. With one of these you should be offered at least four core features. Those include caller ID, voicemail hosted by the provider (meaning you don't need an answering machine), call waiting (essentially a one-line hold), 911 support (sometimes called "E911"), and three-way calling allowing you to reach out to a third participant in any phone conversation. There will likely be a slew of other features available, but they'll differ across quality providers while these four should always be available. Most of these will work in a two-step process:
PhonePower is one of a handful of VoIP providers that actually specialize in residential VoIP rather than business VoIP. Although PhonePower has many plans, it’s best for calling within the US (including Puerto Rico) and Canada. That’s because it has possibly the cheapest prices in residential VoIP, providing you’re calling solely on local numbers. PhonePower also enables calls abroad, although there are cheaper options such as Vonage if you’re planning on making more than an hour’s worth of calls internationally each month.
For the business that needs better tools for allowing collaboration between employees, 8×8 has some strong features. Employees individually can host conference calls, either audio and video calls. They can set up online chats with each other, making it easier to stay in communication, even when they’re out in the field. 8×8 also provides integration with other collaborative tools you may already be using, like Salesforce, Microsoft Office 365, or Google G Suite.
Not every internet connection is VoIP ready, so before you sign up, make sure that your line will provide you with the level of VoIP speed and service you need. You can easily find resources online for checking the speed and call quality of your connection. The quality of your connection can potentially impact the clarity of your calls, so pay close attention. 
VoIP allows both voice and data communications to be run over a single network, which can significantly reduce infrastructure costs. The prices of extensions on VoIP are lower than for PBX and key systems. VoIP switches may run on commodity hardware, such as personal computers. Rather than closed architectures, these devices rely on standard interfaces.[12] VoIP devices have simple, intuitive user interfaces, so users can often make simple system configuration changes. Dual-mode phones enable users to continue their conversations as they move between an outside cellular service and an internal Wi-Fi network, so that it is no longer necessary to carry both a desktop phone and a cell phone. Maintenance becomes simpler as there are fewer devices to oversee.[12]

Similar to Ooma's residential service (below), AXvoice deploys its home VoIP with the help of an appliance, appropriately called the AXvoice Device, which sits between your home's phones and your Internet router. This device not only serves as a bridge between your old phones and the new VoIP service it also enables many of the advanced features that straight POTS bridges often don't address.
Network routers on high volume traffic links may introduce latency that exceeds permissible thresholds for VoIP. Excessive load on a link can cause congestion and associated queueing delays and packet loss. This signals a transport protocol like TCP to reduce its transmission rate to alleviate the congestion. But VoIP usually uses UDP not TCP because recovering from congestion through retransmission usually entails too much latency.[16] So QoS mechanisms can avoid the undesirable loss of VoIP packets by immediately transmitting them ahead of any queued bulk traffic on the same link, even when the link is congested by bulk traffic.
^ White, C.M.; Teague, K.A.; Daniel, E.J. (November 7–10, 2004). Browse Conference Publications > Signals, Systems and Computer ... Help Working with Abstracts Packet loss concealment in a secure voice over IP environment (PDF). Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on. 1. pp. 415–419. CiteSeerX doi:10.1109/ACSSC.2004.1399165. ISBN 978-0-7803-8622-8.

We recognize that not all our readers’ businesses are based in the US. So we took another pass at our content to provide more information on each provider’s international offerings. And because 8x8’s international rates on calls made from the US are so good, we bumped it up to our number five spot. Finally, we added info about Ooma’s new plan (Ooma Office Pro) to the offerings mentioned below.

The Yealink CP960 conference phone strikes an outstanding balance between ease-of-use and powerful features, delivering a smarter audio conferencing solution for your company. The Yealink Optima HD IP Conference Phone CP960, comprising the power of the Android 5.1 operating system. This Y-shape brand new release from Yealink combines simplicity of use with sophistication of features, being perfect for any team environment, especially for medium to large conference rooms. In regard of its crystal-clear audio quality, your conversation will sound natural and bright anywhere. You can connect an external loudspeaker to it if necessary. The Yealink CP960 provides wireless and wired pairing with your mobile staff – smartphone or PC/tablet via Bluetooth and USB Micro-B port.
Ooma advertises only two plans: Ooma Office and Ooma Office Pro. Ooma Office includes unlimited domestic calls, three-way calling, virtual fax machines, plus most of the industry-standard features you’d expect from a leading private branch exchange (PBX) provider. Meanwhile, Ooma Office Pro offers more premium features, including call recording and enhanced call blocking—to name a few. But with either plan, you’ll have to pay a $29.95 one-time activation fee to get your service started.
Yealink DECT repeater RT20U, designed in accordance with Digital Enhanced Cordless Telecommunication (DECT) standard, is widely compatible, easy to install, and a user-friendly display concept. The repeater, base station, and cordless handset employ wireless connection. It can be deployed to extend the DECT radio coverage of all Yealink base stations significantly in all directions. Signals with clear status LED display are exchanged without acoustical, and visual differences.

Nextiva also provides a number of helpful features for businesses working from home. For starters, there’s the Nextiva app, which lets you use your business phone number to make calls remotely from your desktop or mobile devices. Nextiva’s team collaboration tool, Cospace, also lets your team collaborate via video chat, so you can keep everyone one the same page.
If that all is starting to sound more complex than it's worth, remember that turning your PBX into a software solution means significant opportunity for flexibility and integration that you simply can't get any other way. After all, programmers can now treat your phone like an app. Where that's taken us is to the fast-changing UCaaS paradigm (more on that below). Here, traditional VoIP providers, like the ones we review as part of this review roundup, provide additional software capabilities that are all implemented and managed from a single, unified console.

VoIP endpoints usually have to wait for completion of transmission of previous packets before new data may be sent. Although it is possible to preempt (abort) a less important packet in mid-transmission, this is not commonly done, especially on high-speed links where transmission times are short even for maximum-sized packets.[18] An alternative to preemption on slower links, such as dialup and digital subscriber line (DSL), is to reduce the maximum transmission time by reducing the maximum transmission unit. But since every packet must contain protocol headers, this increases relative header overhead on every link traversed.[18]
Whether it's a dedicated bridge device or a special VoIP phone, you'll need something on the hardware side compatible with VoIP in order to access the technology's chief benefit: its software layer. It's at this layer where VoIP's advanced communication and collaboration features are enabled and how well the provider has leveraged those advantages will be directly reflected in how its proprietary hardware and back-end services are programmed. Whether it's a phone or a bridge, if you're worried about getting lost in technobabble when trying to setup your new phone service, remember that the best providers should be able to ship you pre-configured devices that shouldn't require much, if any, intervention on your part. With these, you simply plug them into your router or connect them to your Wi-Fi network and they'll go out and find the provider's network on their own. Just power them up, connect to your network, and wait for the light to turn green.
Signaling – Performing registration (advertising one's presence and contact information) and discovery (locating someone and obtaining their contact information), dialing (including reporting call progress), negotiating capabilities, and call control (such as hold, mute, transfer/forwarding, dialing DTMF keys during a call [e.g. to interact with an automated attendant or IVR], etc.).
In general, the provision of VoIP telephony systems to organisational or individual users can be divided into two primary delivery methods: private or on-premises solutions, or externally hosted solutions delivered by third-party providers. On-premises delivery methods are more akin to the classic PBX deployment model for connecting an office to local PSTN networks.
Companies working from home will appreciate Ooma’s remote features. For starters, Ooma offers a mobile app that lets you make and receive calls from your smartphone using your business number. You can also set up ring groups, which allows you to group extensions together so they all ring simultaneously—then the call gets transferred to whichever remote employee picks up first.
If you're wondering what you get with a softphone that you won't with a standard phone handset, then that depends on the service. Business-class softphones offer all kinds of features related to online meeting collaboration, call routing, multi-line conference calling, and more. From a residential VoIP perspective, you'll most often find video conferencing (though more and more this is becoming a separate product from most providers), a voicemail-to-text converter, detailed call records, and user controls for users other than yourself. Some services also offer faxing, text chat, and call metering so you can see how much you're spending.
Some form of call center capability is often available, though many times either as a different product version or simply a higher pricing tier, so be careful before you assume you'll be getting those features. These capabilities are meant to support large sales or service desk staff and their need to route and process a relatively large number of incoming customer or user calls. That means complex menu trees, an auto-attendant for routing, and service queues. You'll probably find you need interactive voice response (IVR) capabilities, and that should be backed up by support for a live operator or some other type of human intervention.
Most businesses need a portable phone system that can be used anywhere. Of course, landlines do not meet this criterion, and no landline is suitable communication during the journey. The answer is a digital VoIP service that can be used anywhere in the world. All you need is an internet connection and your VoIP phone can be connected to any phone number in the world, whether it is connected to the VoIP network or not.
At the VoIP level, a phone or gateway may identify itself with a Session Initiation Protocol (SIP) registrar by its account credentials. In such cases, the Internet telephony service provider (ITSP) knows only that a particular user's equipment is active. Service providers often provide emergency response services by agreement with the user who registers a physical location and agrees that emergency services are provided to that address only if an emergency number is called from the IP device.
The relevant EU Directive is not clearly drafted concerning obligations which can exist independently of market power (e.g., the obligation to offer access to emergency calls), and it is impossible to say definitively whether VoIP service providers of either type are bound by them. A review of the EU Directive is under way and should be complete by 2007.[citation needed]
Your IT staff will understand the basics of what needs to be done before a VoIP system can be selected and installed. That will include capacity testing on your current pipes and a thorough audit of your organization's network management capabilities to make sure they can support and secure the new flow of VoIP data. But for business-level users, selecting a phone system that will help them keep their various processes moving forward, especially the customer-facing ones, starts with understanding what VoIP really is.