The original iPad's latest software stops at version 5.1.1
Ahh...I guess than I don't think MrRipley's experience is comparable to mine.
To answer your question about the problem:
I have an Ipad2 16gb with 3g. I got the 3g not so much for the cellular data as for the gps functionality. I have used the cellular data from time to time as it is useful when traveling and the ability to buy a month of service without contract or setup charges is great. A few months ago where there used to be bars indicating quality of cell signal there is a permanent "No Service" message. From cursory web browsing there is some indication that it could be a software problem. Oh yeah I am still on ios 6 as I heard of slow down with upgrade to seven, (supposed to be better with later iterations of 7, though anecdotally my friend complains of enfeeblement of his.) I reset my network settings. The ipad says my sim is not provisioned. The reason I strongly suspect the "No Service" message is software related is that my mother has the same Ipad, pretty much unused which now has the same message. The people at the Mac Store said the path is network reset than restore which means upgrade, then hardware which means new ipad.
I guess I have a brief window to upgrade to 7 without learning how to jailbreak as with the 8 screwup apple still signs their end of a restore with 7 but I have to find a safe place to get it and figure out how to put it into itunes etc. to do the restore upgrade. I feel fairly certain that if I get 8 my experience will be like Skuzzy's. I'd rather have the functionality that I have, (for as long as it lasts,) than a brick with cell service.