Two difference GSM network exchanger

Sell 2 difference GSM network exchange for difference region to save fee
2 line GSM telephone can be auto-transfered, when you(A place) dial one line phone number to the base(B place), the base test and pick up anther line, you will hear anther dialling tone, you can dial the phone(C place) number again.
Used in borderline of country or difference region to save fee!