Only the phone company may change the destination. You will have to decide how fast a connection you will need. The minimum speed is 56 kbps, which is perfect for a small business. If you plan on transferring audio in real-time, you will need a 1.54 Mbps line, commonly known as a T1 line. If you plan to transfer video in real-time, you'll need a T3 line which transfers data at the rate of 45 Mbps.
Dedicated lines come in several different flavours.
Analog lines can handle speeds up to 28.8 kbps. This is the same grade as your typical home phone line. You probably don't want one of these. The cost of a digital line depends on the distance between you and your service provider. An alternative to digital dedicated lines is frame relay.