Motorola codes are 000000 and 1234. If these codes doesn't work then try asking him if he has changed the code manually. If that doesn't work either then check if he has bought the phone from Airtel under some scheme. In such cases usually Airtel locks the phone in such a way that no other SIM (From other Service Provider & even Airtel also) can be registered or activated from that handset. See if that is the case with you.
Hope these three solutions will solve your problem.