Using US iphone in Thailand?

I apologize if this is rather complicated-

I'll be volunteering in Thailand somewhere that requires a phone and has no internet access. So I'm trying to figure out what would be the best option.

I have an iphone 5c that is currently on contract with sprint, and I'll be going to Thailand while it is still on contract. Is there anyway to use this phone with a SIM card while in Thailand without messing anything up?

If not, I also have an old iphone 4s that is in rather terrible shape (cracked screen, horrid battery), but it is not on contract- would it be cost effective to get the screen/battery fixed/jailbroken/sim card inserted?

Or are there phones already in Thailand/that I could buy now that are less expensive/easier than all of this?

You can buy a phone In Thailand for less than $50 then go to any 7/11 store and buy a 500 baht card for $15. You can call the US for about 7 baht per min.

Your I phone will not work here unless you have it unlocked, which you don't want to do and I don't blame you for that. To get the other phone fix will cost you more money than it would cost to buy a cheap phone here or a used phone here for what you need it for. I don't understand why someone would say get a ipad when you said you have no internet access where you going to be. Seems like someone isn't reading what you wrote.

Just go to MBK Mall in Bangkok, they have thousands of shops on the 4th floor selling new and used phones. You can get a new samsung phone for $20 here or a used one even cheaper. Than just purchase a sim card. Also make sure you have your passport with you to register the sim. I recommend AIS 1 2 call sim, you can buy one when you buy the phone and top it up at any 7 11 store. I purchase one of these phones for my daughter and son when they visit me here.

Hope this helped.

My advice is to bring the old 4s.

or you could bring the 5c and have it "unlocked" for $10 - that means you can use any SIM card on it & it has been registered with Apple iPhone company. Just go to Panthip Plaza mall in Bangkok or MBK mall.

honestly, i'd just buy a generic brand tablet PC for about $40 with SIM card 3G included and one month of unlimited download from Panthip Plaza. You can either take it back with you and use for future trips or give it as a present to a kid before you leave.

Best plan is to buy a cheap phone from vendor inside Thailand and also a SIM. You can get pre-paid phone plans best for you then.
I ask you to avoid AIS because of its connection with a criminal billionaire who has hurt Thailand greatly. This is only ethical, not technological. There are other good services available.

Shop called MBK in the center of BKK is telephone heaven but Tesco Lotus and many other shops sell too. 7-11 have SIM.
Company called TRUE has kiosk in many Tesco shops.