VoIP can technically work on any Internet connection, but you will need to ensure that you have enough bandwidth to cover your call volume. An over-simplified formula to determine bandwidth is to take the standard 80K of bandwidth needed to make one call and to times that by the number of users you have online at any given time. Compression ratios can help you reduce your bandwidth requirements if the load becomes too great.
In reality you need a minimum of a DSL or Cable line, but compare your answer to the equation above to the capacity of different business-grade connections:
- ISDN: 64 Kbps to 128 Kbps
- DSL: 128 Kbps to 8Mbps
- CABLE: 512 Kbps to 20 Mbps
- T-1 line: 64 Kbps per channel or up to 1.544 Mbps