In the USA, Verizon and Sprint sell terminals iPhone 5 decoded which seems to work on 3G networks all over the world, but in the case of Sprint there is a small problem. Specifically, the terminals I can not send SMS when they are used on other networks than the one owned by Sprint, this being a not very nice method to block an extremely important functionality of a mobile phone and unfortunately solving the problem is not easy.
Considering that the terminal cannot send SMS from outside the US, the iMessage and FaceTime services cannot be activated in the case of a restore because their activation involves sending an SMS to Apple. Even if the problem is theoretically related to iOS and not necessarily to Sprint, you could still solve it by sending an email to this email address: support@apple.com. The email should be sent from the address used for the Apple ID associated with the iPhone and it should contain: the serial, imei, model, MEID and phone number of your iPhone, all these together with a scan of the purchase invoice and possibly with the name of the store where you bought it.
After sending the message, the problem should be solved in a few days, but if you don't have those details, the chances of success are quite small. The MD657LL/A – MD656LL/A – MD661LL/A – MD660LL/A – MD668LL/A -MD667LL/A iPhone 5 models have this problem and it would be ideal to avoid them.
