Although jitter is a random variable, it is the sum of several other random variables which are at least somewhat independent: the individual queuing delays of the routers along the Internet path in question. Motivated by the central limit theorem, jitter can be modeled as a gaussian random variable. This suggests continually estimating the mean delay and its standard deviation and setting the playout delay so that only packets delayed more than several standard deviations above the mean will arrive too late to be useful. In practice, the variance in latency of many Internet paths is dominated by a small number (often one) of relatively slow and congested bottleneck links. Most Internet backbone links are now so fast (e.g. 10 Gbit/s) that their delays are dominated by the transmission medium (e.g. optical fiber) and the routers driving them do not have enough buffering for queuing delays to be significant.[citation needed]
For instance, while AT&T offers landlines with unlimited phone calls for $33.99/month, with RingCentral you can get the Essentials plan, which includes unlimited phone calls starting at just $19.99 per person per month, and you can also enjoy a more extensive list of features. On Grasshopper, the introductory plan costs as little as $26/month, but that includes 3 extensions. With residential VoIP, you have a bundle of features you couldn't find with traditional landlines. Also, because of technology's continual advancements, the features continue to improve every year without a sharp rise in costs. VoIP for home use makes sense because you derive so much more value than what the traditional phone companies of today are offering.
Overall, VoIP is simply the better option for the vast majority of customers. Dropping your landline means no more hidden fees or metered long distance calling charges. Everything is charged at one low rate by most providers and your ability to customize your phone service to exactly what you need is far greater. Unless you've got some highly unique circumstances that somehow mandate a landline, VoIP is simply the better choice.
Like the rest of us, you probably don't like to get hassled with unwanted phone calls when you’re at home. You can also implement “enhanced call forwarding” to reroute and block the numbers that you specify, without the caller having any idea. You also can set up your phone to block international and directory assistance calls, so they don’t bother you at home. 
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.  
The only additional piece of equipment that you need is an Analog Telephone Adapter (also referred to as an ATA) that allows you to connect your existing telephone to your home Internet. This equipment is typically provided on a free lease basis from the home VoIP provider that you choose, or you can use you own device if you prefer. You can also use IP phone(s) instead of using the ATA with your existing analog phones. The sound quality is better but there is more up front cost as IP phones are more expensive than the ATA devices.