"cellphone" shield?

OK, but remember that the GSM module will draw more power than the USB port can supply.

Yes, thanks.
The set up is running from a 12v 2.5a Supply, into Vin.

The Unit will always send the first SMS without a problem.
The second and subsequent SMS's fail with a error message from the SM5100.

The error is as listed before CME Error 4 (an unknown command error).
I can still query the unit, and get an answer, using other queries, like AT and I get OK.

There is something I cant find getting in the way of the next message.
Like an unfinished command getting fed into the sm5100 before I start the SMS sending loop.

Does any one have a working code example?
IE push a button and send an SMS.
I would love to see one, and test with my hardware.

MH