I have been toying around with GSM modems for some time – working on the Rotary Cellphone project, i settled on the SIM900-module from SIMCOM.
Early in my quest, i mistakenly read, that the SIM900 was Dual band, and the SIM900A was quad band. As I decided that i did not need the Quad-band capability, i ordered the SIM900A-modem, as it was a few $ cheaper.
Ordering the first module from far east (AliExpress) my choice was the SIM900A model. I milled a breakout-board for the GSM-module, soldered it on, and everything “seemed” to work, but i could not register the modem on the Danish GSM-network. It acted like it was locked to a specific GSM-vendor.
The modem being brand new, ruled out the option that someone else had a go at it, so what was happening ?
I trawled the documentation at SIMCOM, and couldn’t readily find any information on what the differences between a SIM900 and a SIM900A-model were.
Some helpful people at the local Hackerspace mailing-list soon found the culprit (i guess their Google-fu was better than mine)
The SIM900A-model is locked to these regions:
- East Timor
Official documentation is mirrored here: SIM900A Supported MCC List V1.00
Why SIMCOM makes this module, locked to specific regions, i do not know, if you have any idea why, please leave a comment.