GSM can't find OpenBTS network

I'm using a USRP1 system with 2 RFX 900, no hardware alteration have been applied.Also using GNU-radio 3.1.3 and openbts-2.6.0Mamou. OpenBTS installment was successful and able to use OpenBTS. In addition I edited GSM.MCC to 505 and Band to 900. However the Mobile, Nokia C2-00 and Motorola KRZR K1, were unable to detect the OpenBTS network.

Ahmed AL-Kalbani