The service often seen at different sites works in such a way that you
need to enter your telephone number in a special window and after some seconds
you and the company representative will receive a call, which will allow you
communicating.
By using Portech SBK-32 expander for 32 SIM-cards, you can increase the number of channels in the Portech MV-37X GSM VoIP gateway series using the Internet.