Its no good to you for the other GSM shields, Sorry.
I spent so, so long hacking at this stupid shield trying to make sense of the +SIND's and other rubbish - these things do work, they just test your patience. The minimal and poorly written documentation is useful if not as frustrating, hopefully this will save you some time.
Dont take this all for gospel, Im not an electronics or programming whizz, I have just persevered and learnt a few things.
Please feel free to question anything written here and Ill try to update the instruct-able if you can contribute.
Step 1: Things to consider
I have found some good resources,
The most useful being some actual working code:
A good intro into setup
Some things to note:
1) Software serial is not the best option, in my tests it doesn't keep up with the serial output from the GSM module, and if you cant keep up then the data is dropped and your stuck. Software serial is ok for grabbing the return codes from your AT commands but when it comes to receiving your actual data, like http responses - it just doesn't keep up at all. I have seen mention that the 9600 baud rate that the SM5100B-D is set to is not fast enough, I have not found this to be true, as long as I use a hardware UART I get all the data back from the shield.
2) Power - you cant run this shield from the Arduino Power - you just cant. I tried to ignore these warnings, dont waste your time. Feed it 5 volts from a transformer or battery capable of supplying 2-3 amps. You will find that if you dont it will just keep overdrawing on your Arduino when it goes to transmit and everything will just reset.
3) Antenna, you need one.
I have actually been able to get +SIND:4 without one, but I have been getting full reception with one of those tiny little duck Antennas - I got two for a couple of dollars right here:http://www.electrodragon.com/?product=quad-band-ce... For Australians - You can pick up an antenna from Jaycar - pricey but dont have to wait on delivery: http://www.jaycar.com.au/productView.asp?ID=AR3310
4) Documentation, the official AT command set documentation comes in handy, only the author truly knows what on earth he/she was trying to describe, its bad, real bad, but it comes in handy: https://www.sparkfun.com/datasheets/CellularShield...
I guess sparkfun wrote this more specific GPRS / IP stuff, as it kind of makes sense in comparison: