SIP Trunk services in the your zip code are provided from local carriers, as well as the installation and provisioning, hardware and software. Traditional, analog voice calls use copper wiring, meaning one voice call per line. As businesses grow, it is expensive to add more lines just for each added phone. However, installing a larger, digital-capable line like a T1 line is also expensive. It is something to consider as your business grows. If you expect to be growing fast, it would not be worth installing more copper lines just to throw them out down the road. Installing a T1 line may be expensive now, but as you grow, it becomes less and less expensive.