If you want to forward incoming calls, coming to TezGSM, to any other number, you should use the Call Forwarding service.
The service is free of charge is the forwarding is set onto the number, belonging to a country with no extra rate (see the rates on the site).
In order to activate the service dial the special code *146*081*00<country code><number># and push the button "Dial".
In order to deactivate the forwarding, dial *146*080# on your TezGSM number.
IMPORTANT: Short messages will not be forwarded.