In previous blogs on this site, we have made reference to the various types of services that are available to customers with business telephone systems. When talking about phone line contracts expiring with an existing carrier, Eric Moore pointed out that there are many alternative options available to the customer, depending on the volume of phone calls that need to be accommodated, and what services are provided in that specific geographical location. Additionally, I had explained in my blog about the voice quality of VoIP telephone systems that the voice traffic coming from such a system to a destination outside of the system is carried by the services of the local dial tone provider (as opposed to over open Interenet).
If you are a smaller company in a business sector that does not require a great deal of call volume, individual telephone lines will be sufficient for your business. However, if your call volume dictates that you need as many as 10-12 or more paths for simultaneous conversations, it may be more efficient and economical to have your voice paths delivered via a digital or IP service. Similarly, if your business requires individual phone numbers (Direct Inward Dialing) for each person within the company, or if you depend heavily on multi-party conference calls, an alternative to analog telephone lines is also in order. Lastly, if you have special needs for your internet bandwidth in addition to your dial tone, there are combination services using digital or IP delivery which may be appropriate as well.
Most carriers - whether it is AT&T, another Local Exchange Carrier, or even one of the cable companies (Comcast, Cablevision, Cox, etc.) - are now providing dial tone via digital PRI circuits. A PRI will provide you with 23 channels for inbound and/or outbound phone calls, and the carrier can provide as many telephone numbers as you may need for Direct Inward Dialing. This becomes an economical alternative (based on cost comparison) if you are already paying for ~12 or more individual phone lines. If you do not require the call volume of 23 voice channels, but still have a need for Direct Inward Dialing phone numbers, SIP Trunks are another delivery option for your services. Not every carrier currently offers SIP trunks, but for those that do, they are able to provide dial tone via IP to your business telephone system, and can customize the amount of call paths to meet your needs (not confined to exactly 23 as with a PRI). While not as widely available, SIP trunks become a more economical option even if you have fewer than ~12 individual phone lines.
As you can see, if your business is of a certain size, and has certain needs, alternatives to basic analog telephone lines can be a very attractive option.