On the phone providers' side, since this review roundup was first published, some of the products listed here now belong to other companies and some have merged into new products. If you're planning to depend on your phone system over the course of the next decade, then you should consider a vendor that's stable enough to still be around when it's time to up upgrade.

SIP is built to work on a peer-to-peer (meaning endpoint to endpoint) basis. Those two points are called the "user-agent client" and the "user-agent server." Remember that those points can be swapped, so that in SIP, the endpoint making the call is the user-agent client initiating the traffic and endpoint receiving the call is the user-agent server receiving the call.
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.
Such emergency services are provided by VoIP vendors in the United States by a system called Enhanced 911 (E911), based on the Wireless Communications and Public Safety Act of 1999. The VoIP E911 emergency-calling system associates a physical address with the calling party's telephone number. All VoIP providers that provide access to the public switched telephone network are required to implement E911,[34] a service for which the subscriber may be charged. "VoIP providers may not allow customers to "opt-out" of 911 service."[34]
As always the best place to start is at the beginning! The following buttons provide access to some of our best guides and tools for getting started with VoIP. These articles give a great background into VoIP, help you understand all the basics, and answer most people questions. The VoIP/Speed test tool performs a test of your Internet connection and provides a great indication of how well VoIP will work at your home. We highly recommend running this test.

The benefits of making the change permanently from a traditional landline phone to VoIP phone services can have a lasting effect — minimizing cost and maximizing customization. Turning your home into a fully integrated network, VoIP is the most economical and intelligent method of making phone calls. Doing away with your landlines means doing away with fees and long distance charges in favor of one low monthly rate. The sooner you do away with landline service, the sooner you’ll be enjoying more features for substantially less, saving hundreds of dollars a year. Make the switch, and leave those switchboards in the dust…you won’t regret it – Get VoIP!

Disclaimer: The information featured in this article is based on our best estimates of pricing, package details, contract stipulations, and service available at the time of writing. All information is subject to change. Pricing will vary based on various factors, including, but not limited to, the customer’s location, package chosen, added features and equipment, the purchaser’s credit score, etc. For the most accurate information, please ask your customer service representative. Clarify all fees and contract details before signing a contract or finalizing your purchase.
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.
Softphones are increasing in importance in VoIP offerings to the point that for some they're the only choice. They are a critical part of UCaaS and are as common on mobile phones and tablets as they are on desktop PCs. For workers in call centers, softphones are a common tool because of they're the front-end window of any CRM or help desk integration. So, for example, a softphone can combine a telephone conversation with text chat and screen sharing, which means a conversation between two employees can seamlessly add more participants, handle private text chats between those participants while the call is still going on, and extend to a collaboration session in which the group shares screens, documents, and data—no prep, no reserved lines, just button clicks.  
1992: InSoft Inc. announces and launches its desktop conferencing product Communique, which included VoIP and video.[85] The company is credited with developing the first generation of commercial, US-based VoIP, Internet media streaming and real-time Internet telephony/collaborative software and standards that would provide the basis for the Real Time Streaming Protocol (RTSP) standard.[86][87]
The following table provides a high level summary of how residential VoIP service compares to other alternative solutions for home phone service. The table compares this service to a regular landline, a bundled phone service from a cable company such as double or triple play, and a cell phone service. The cell phone is included as some people decide to just get rid of their wired phone and use their cell phone for all calls. Free services such as Skype are not included as they are not effective, like for like, landline replacements in our opinion.