SIM800C registration problem

Hi
I am using a SIM800C module in an embedded environment.
The SIM800C is powered with a 3.6V primary Lithium cell and am using a boost regulator TPS63000 for boosting up the supply to 4 V.
The problem I a facing is a peculiar one. The system works very well in our lab at Pune and can send sms/gprs data perfectly fine. No issues at all with network registration etc. But when the same set up is shifted to Hyderabad, it fails to register. I tested the SIM cards used in Hyderabad in Pune and it works very well. But it fails to even register at Hyd.

The status LED blinks once and goes off. Nothing happens after that.
The TPS63000 has a shutdown pin, which i am using to power up the GSM module supply then wait for 1s and give the power on command to the module.

What could be the issue?
Regards
Surendra

The module draws more current when signal is weak. See if the place they are using it is having good signal strength as in your area of testing in Pune.