[Eight Ball]

No money owed on an iPhone 4S, but not the original purchaser and no proof of purchase, but IMEI is clean.

Can it still be used on Cricket or Net10 (or other AT&T MVNO's), and will it still get iOS OTA's? For instance, I think the 4s is getting the next version of iOS. Would the phone get them still if on an MVNO?

I suppose while am asking, I suppose I should ask if the phone can even be on AT&T GoPhone PrePaid. So long as the IMEI is clean would that pose any problem? Thx!

[warcraftWidow]

Getting an update to the new iOS version has nothing to do with the carrier. Do it will/can get iOS 8 when it is out.
ATT would probably have the best answer on whether it can be used on their MVNOs. It might need to be unlocked but if it is fully paid for and not under contract, then you should be able to get it unlocked.

[OBF]

I would think that it should. We know that AT&T bought Cricket and I get AT&T's coverage even though I have Cricket service so if you have an AT&T phone, I don't see why it wouldn't work with Cricket either. You may want to ask them though.