Hi I recently changed the sim in my pay monthly iphone 5 and put the pay monthly sim in another phone (not an iPhone) and now iMessage doesn't work with the new sim?

It needs to re-register, try turning iMessage off and on in settings.

iMessage is so shit.

It really isn't though.

EDIT: I should quality my reply a bit, otherwise it's no more constructive than the 'iMessage is shit' post.

Reasons I like iMessage:
[LIST][*]It integrates directly into the Messages app but is completely optional. [*]It incorporates deliverd and read receipts.[*]It doesn't compress pictures into awful quality like WhatsApp. [*]It will automatically send messages as texts if it has to. [*]It syncs messages between my iPhone and iPad.[/LIST]
Granted, it's single platform so only any use on iOS, but since it's something integrated into and above and beyond the standard text messaging app, that doesn't really matter too much. Also, it has suffered from a few outages recently, though none particularly sustained.