It seems that Sprint clients have the same bad experience using their phone trying to send SMS on gsm local network, see here the unfortunate experience of this Sprint client https://discussions.apple.com/thread/4371703?start=45&tstart=0
"I got a Sprint iPhone 5 on contract and then called sprint and told them that I needed to get the phone unlocked cuz i was going to travel to Mexico City. i did this with my iPhone 4s and I never had a problem with it overseas. Sprint NEVER said they can’t unlock it, in fact the international department was very nice and said "yes, just restore it and you should be fine" i did that and i got a message on iTunes that said that the iPhone was unlocked.
When i called to do the same with the iPhone 5 i got the same response but this time when i did the restore, the iPhone is unlocked message did not come up. i called sprint again and they said that they were having problems unlocking the iPhone 5s and that they send the request to apple but never get a confirmation that the device is unlocked on their end like they did with the 4s.
They told me they would contact me later and eventually a manager emailed me and asked that I do the process again. I had the same result and just left for my trip, when I got to Mexico City I put in the sim card and the phone started working no problem, so i thought that the phone had been unlocked successfully. Unfortunately I have the same problem that you all do and I can’t send sms to anyone.
, after having their device confirmed unlocked from Sprint service for international use, some one has an update on what's going on with this problem ?..."
WHAT'S GOING ON WITH THIS PROBLEM SPRINT ?
Nobody in Sprint company can give us information ?
Sorry for the delayed response. For a situation like this we need to get assistance from our International Support group. I will send you a private message with information on how to contact them, or if you prefer I can contact you directly and conference them in to ensure we get the support you need.
I'd like to find out how to resolve this issue about unlocking my iPhone5 for international travel too. I just got mine yesterday and need to make sure that this issue has been resolved before my 14-day return period passes. Sprint- please let me know how to get this addressed so I don't have to return my device. I heard Verizon releases theirs unlocked right out of the box.
I have the exact same issue with My iphone 5 that is internationally unlocked here in Egypt I cant send sms Messages SPRINT This is a JOKE