GSM SIM 900A

Hello, I am from Nepal, I have been using GSM SIM 900A for the smart meter operations. GSM SIM 900A with a serial number: S2-1040V-Z1K0B with version 3.9.2 works in Nepal besides the same version, other version as well as GSM SIM 800 module doesn’t works I want to know why the different version does not work in Nepal. I have been trying to carry out sms and call operations in different version of sim 900A module with different part number but it does not response to the input AT command of sms and call. I want to know why this is happening as well as if there is any data sheets regarding the various version.