Business phone services can be confusing as they have two major aspects: interface and transport method. The interface should match your phone system. The transport method will affect redundancy, flexibility, and quality.
1) POTS – POTS (plain old telephone service) are the traditional phone lines for small businesses and homes. POTS typically works for small offices but scales poorly and offers fewer features.
2) PRI – PRI is a digital service offering up to 23 channels (calls) over a single circuit, including caller ID and Direct Inward Dial (DID) services.
3) SIP – SIP is a specific form of VoIP, like PRI it offers caller ID and DID but you can order any number of channels to scale perfectly to your capacity needs. SIP also has the advantage of not needing a costly PRI card, however not all phone systems support SIP.
Most of the services above can be delivered via traditional copper delivery or SIP delivery. SIP (VoIP) delivery can bring the cost advantages of VoIP to traditional phone systems, by converting SIP delivery to POTS or PRI interfaces. Some businesses may prefer the simplicity of traditional copper services and keeping voice and data services separate.
Long Distance, Toll Free & International
Of course long distance, toll free, and international services are an important part of any business phone service. Many people believe VoIP has “free” long distance, but in reality they charge extra per line for “unlimited” long distance (see the contracts, its not unlimited). Picking metered services, bundles, and unlimited services is an important decision which varies highly by each customer.