Hi.
I've had the same problem on my 3rd gen Ipad running ios 6.1.2 for a few week now i.e. push notification message, can't log into iMessage & FaceTime, also Find my iPhone doesn't find my Ipad even though location services are on.
I have no idea why this has happened and have never upgraded to ios 7.
I am not a developer & I do not use iCloud for backups
I activated my Ipad via ITunes when I first bought it a couple of years ago and am fairy sure that I have activated it whenever I upgraded the ios to a newer versions of IOS.
Looking through this thread it appears that the redsnow fix would resolve the issue for me as you no longer need to be a developer on ios 7 for it to work and after applying the fix I should be able to connect my ipad to iTunes and activate it.
However I'm still nervous about doing this after comments from several members that they were not able to re-activate using iTunes.
Taking all of the above into account, would really appreciate it if anyone can confirm that the redsnow fix should work for me and that I will be able to re-activate my device using ITunes.