Configurations
of GSM/VoIP networks allow the service providers to avoid the local Wired
Public Switched Network (PSTN) in communication with a GMS mobile handset. As a
result, the high rates charged by telephone companies are avoided.
The service offered by telephone companies allowing creating the telephone numbers on the same line where the existing number is. The call tone for every number will be different from another. There is also an opportunity to program a custom ring tone for the incoming call.