Hello, I am from Nepal, I have been using GSM SIM 900A for a smart meter that I have designed to work with my solar PV system. The GSM SIM 900A that I have used in my first prototype (having the serial number: S2-1040V- Z1K0B with version 3.9.2) works well in Nepal. Except this version, none other version seems to work. I have tried using several other versions of GSM SIM 900A and GSM SIM 800 module as well. I want to know why the different version does not work in Nepal. I want to order a bulk of these GSM SIM 900A for testing now, but I am not quite sure which version to order. My supplier in China is confused as to why other version of SIM900A is not working. Could anybody let me know why this is happening ? How can I be sure that the SIM 900A would work in Nepal when I am ordering from suppliers in China ? It would be great if any helpful souls could enlighten me in this matter ?