Generally, telephone service via residential VoIP is either free or costs less than similar service from traditional sources, but it's comparable to alternative Public Switched Telephone Network (PSTN) service providers. Some cost savings are from using a single network to convey voice and data, especially where users have accessible underutilized network facility they can use for residential VoIP at no extra cost. VoIP to VoIP telephone calls on any given provider are customarily free, while VoIP to PSTN calls normally costs the user of residential VoIP.
Generally, telephone service via residential VoIP is either free or costs less than similar service from traditional sources, but it's comparable to alternative Public Switched Telephone Network (PSTN) service providers. Some cost savings are from using a single network to convey voice and data, especially where users have accessible underutilized network facility they can use for residential VoIP at no extra cost. VoIP to VoIP telephone calls on any given provider are customarily free, while VoIP to PSTN calls normally costs the user of residential VoIP.

VoIP technology does not quite require broadband Internet access, but this normally sustains improved quality of service. A considerable percentage of homes today are connected to the Internet through DSL, which requires a traditional landline telephone line. Having to pay for provider residential VoIP as well as both a basic landline telephone line and broadband Internet access minimizes the probable benefits of VoIP. However, some regional telephone companies now offer DSL service without the telephone, consequently saving subscribers money when they switch to provider residential VoIP. VoIP can also be used with Cable Internet instead of DSL, which can eliminate the need for a traditional telephone line completely.
Some broadband connections may have below looked-for quality. Where IP packets are lost or delayed at any point in the network between residential service VoIP users, there will be a momentary drop-out of voice. Technology has improved the reliability and voice quality over time and will continue to improve residential service VoIP performance as time goes on.
Issues with enterprise IP telephony
Although only a small number of office environments use a pure VoIP infrastructure, telecommunications providers regularly use IP telephony. This is often used over a devoted IP network, to connect switching stations, as it converts voice signals to IP packets and back. The aftermath is a data-abstracted digital network which the provider can upgrade and utilize for multiple purposes.
Corporate customer telephone support often uses IP telephony strictly to take advantage of the data abstraction. The benefit of using this technology is the d esire for only one class of circuit connection and better bandwidth usage. Companies can acquire their own gateways to abolish third-party costs, which is worthwhile in some instances.
VoIP is widely employed by its carriers, chiefly for international telephone calls. It is regularly used to direct traffic starting and ending at conventional PSTN telephones.
IP packets are sometimes lost or delayed at any point in the network between VoIP users. This usually results in a temporary drop-out of voice. It is more noticeable in severely-congested networks and where there are long distances as well as inter-working between end points, such as in corporations.
Requirements for home users and corporations
A major development starting in 2004 has been the introduction of residential VoIP services over broadband enterprise service VoIP, in which subscribers make and receive calls as they would over the PSTN. Full phone residential VoIP service telephone companies usually provide inbound and out bound calling with Direct Inbound Dialing. A popular offer is unlimited calling in the U.S. and Canada as well as selected regions in Europe and Asia for an even monthly fee.
These services take a wide array of forms which can be more or less similar to traditional Plain Old Telephone System (POTS). At one extreme, an analog telephone adapter (ATA) may be connected to the residential VoIP service and an existing telephone jack in order to provide service nearly identical from POTS on all the other jacks in the residence. This type of service, which is fixed to a single location, is simply offered by broadband Internet providers like cable companies and telephone companies as a cheaper flat-rate traditional phone service.
Often the phrase "VoIP" is not used in peddling these services, but instead the industry has marketed the phrase "Internet Phone" or "Digital Phone", which is aimed at average phone users who are not really tech-savvy. In the corporate workplace, broadband enterprise service VoIP generally uses the term "Internet Phone". Typically, the provider publicizes the advantage of being able to keep the existing phone number. Examples of this type of service in the United States are not limited to Time Warner, Comcast's Digital Phone, Verizon VoiceWing and AT&T CallVantage.

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