Sim900 GSM/GPRS shield from ebay

Hello, I know there are other posts about this topic but, I am such a beginner that they are all way over my head. I need an explanation similar to that of a 5 year old. So, I apologize for the repost.

Background I purchased this shield from ebay ( Attempting to use it with an UNO R3 I got an AT&T go phone with a 3G sim card

After following the provided wiki ( it is clear that something beyond my knowledge is wrong.


Does it require a 2G sim card and I have 3G? RX and TX are pin 7 and 8. I have the jumpers on the SWserial side. What is this com tool I keep reading about and why doesnt it exist for mac? There seems to be a million libraries, which one do I need? Indicator lights -RED is solid - GREEN flashes 3 times/second.

I know its a drag to go through this with such a beginner but please, I am in need of some help.

New developments have been made. Ive figured out the whole serial communication bit and am now having some connectivity problems. After firing up the shield i get the following read out.

+CFUN: 1



Here are the results to CREG, CBAND and COPS.


+CREG: 0,0




+COPS: 0

OK When I try to send a text, i get the following. AT+CMGF=1

OK AT+CMGS = "+1404****863"


Any suggestions to get it working?

Hi, The GSM shield you have purchased uses a SIM900 chip. This chip only works with 2G SIM's and will not work with the 3G network. I had the same problem myself until I worked this out.

The specs are listed it reads Compliant to GSM phase 2/2+ as far as I can tell this means that SIM900 only supports 2G networks. I have managed to get my shield which is also based on the SIM900 to work with a 2G SIM but it will not recognise the network with a 3G SIM.

Indicator lights -RED is solid - GREEN flashes 3 times/second.

The Green led will be the Network status when it is connected to the network correctly it should flash only once every 3 seconds.

This application note may be of interest

I have collected some manuals for the SIM900 which may help

If you need a 3G sheild take a look at this

Good luck