The term PBX spawns from the original term PABX, which is an acronym for Private Automatic Branch Exchange. Essentially a PBX is a private telephony switch that enables a business to operate a phone system with less phone lines than they have employees. This helps organizations take advantage of the natural economies of scale that begin to occur as headcounts rise.

Over time, the PBX has grown to incorporate advanced features such as voicemail, unified messaging, auto attendant (Interactive Voice Response), automatic call distribution (ACD), call queuing, telecommuters, softphones, computer telephony integration (CTI), and more. These features let companies receive incoming calls efficiently; promote more effective interaction among employees; and help sales and call center organizations manage calls professionally. PBX features allow smaller companies and teams to sound and function like large enterprises.

Designed with growing business in mind, PBXtra is a feature-rich turnkey system that is scalable, fully supported, and costs 40 to 80 percent less than comparable systems.

In the traditional world, a PBX typically needs to connect to one or more PSTN (Public Switched Telephone Network) lines, Integrated Access T1/PRI lines, to make outbound calls.

In a VoIP PBX system, you can not only make outbound phone calls via PSTN, and T1/PRI, but you can also make calls via VoIP services provider (with services such as SIP Trunking).

Fonality PBXtra gives you the most flexibility to choose your telephone service type and service provider. You can choose your existing PSTN (Public Switched Telephone Network) line, an Integrated Access T1, or a VoIP service. If you use your existing PSTN line, you'll need to order a server that includes a Base Analog Expansion Card and as many Analog Line Ports (FXO ports) as you want PSTN-lines to connect. If you want to connect to a T1/PRI line, you'll need to order a system with a T1 interface card. If you choose to use a VoIP service, Fonality PBXtra provides you with the ability to use VoIP-only or a combination VoIP and PSTN service with our unique PSTN-Fallback feature. Fonality recommends that you keep at least one PSTN line active so that your main office stays operational in the event of an Internet outage.

An IP (Internet Protocol) PBX is a telephone system that utilizes the Local Area Network and the Internet to deliver calls via data packets instead of the traditional phone network.

VoIP(Voice over Internet Protocol) is simply the transmission of voice traffic over IP-based networks. The Internet Protocol (IP) was originally designed for data networking. The success of IP in becoming a world standard for data networking has led to its adaption to voice networking.

VoIP has become popular largely because of the cost advantages to consumers over traditional telepone networks. With traditional phone service, users in the US pay a flat monthly fee for local telephone calls and a per-minute charge for long-distance calls. On top of that, they usually have to pay a flat monthly fee for Internet connections. Using the Internet connection for both data traffic and voice calls allow consumers to eliminate phone line monthly payment. In addition, VoIP calling plans usually do not charge a per-minute fee for long distance calls within the US and Canada, and have very low international calling rates.

There are three methods of connecting to a VoIP network:

1. Using a VoIP telephone
2. Using a "normal" telephone with a VoIP adapter
3. Using a computer with speakers and a microphone

VoIP telephone calls can be placed either to other VoIP devices, or to normal telephones on the PSTN (Public Switched Telephone Network). Calls from a VoIP device to a PSTN device are commonly called "PC-to-Phone" calls, even though the VoIP device may not be a PC. Calls from a VoIP device to another VoIP device are commonly called "PC-to-PC" calls, even though neither device may be a PC.

A SIP Trunk is primarily a concurrent call that is routed over the IP backbone of a carrier using VoIP technology. SIP Trunks are used in conjunction with an IP-PBX and are thought of as replacements for traditional PRI or analog circuits. The popularity of SIP Trunks is due primarily to the cost savings of SIP, along with the increased reliability as backed by the SLAs of SIP Trunk Providers.

SIP Trunks are cheaper than analog circuits while maintaining the same service quality that businesses expect from line quality. SIP Trunks cost approximately $20 to $30 per trunk, versus $40 per analog circuit. In addition, long distance termination charges associated with SIP Trunks are much cheaper than traditional analog or TDM rates.

SIP Trunks realize their primary benefit over PRIs from cost savings. SIP trunks typically cost $20 to $30 per trunk for unlimited inbound and local calling along with a long distance rate that can be under 2 cents per call. When coupled with line oversubscription (e.g. a 30 person company purchasing just as many SIP trunks as they anticipate having concurrent calls....typically 8 to 10) SIP Trunks are a very cost effective way for a business to save money. Lastly, a primary benefit of SIP Trunks over PRIs is that SIP Trunks can be purchased in increments of 1, whereas PRIs have to be purchased in increments of 23 channels.

SIP Trunks can work with a SIP-ready PBX. SIP Trunks can also be made to work with traditional analog or key systems with an IAD (Integrated Access Device). The SIP Trunk service provider will need to interoperate with the underlying equipment manufacturer. However, it should be noted that with the advent of standards around RFC 3261 and SIP Connect, the challenge of finding SIP Trunk Service Providers with SIP Trunk compatible equipment is significantly decreased.

SIP Trunks are virtual circuits delivered over an Internet Access line. Depending on the number of SIP Trunks purchased, and the amount of excess Internet connectivity, a business should consider purchasing more Internet Access. However, it's important to know that when a SIP Trunk is not being used, the bandwidth otherwise allocated to a SIP Trunk is freed up for use in less intensive applications, such as e-mail and general web use. This dynamic allocation of bandwidth is yet another feature of SIP Trunks versus more traditional technologies, such as analog or PRI circuits.