BUY PREPAID ATT PHONE CARD

If the phone is locked to a particular network you will need to get it 'unlocked'. Depending on how new your handset is most good phone repair shops will be able to unlock it for a small charge.

Your gonna have to buy a prepaid sim card for phone . Once inserted in new phone follow the directions inside sim card packaging.

If both are AT&T phones definitely it should work. If not your SIM might be damaged.

You need to contact the cell phone provider that supplied the prepaid SIM card and ask them if this is possible. Cell phone providers have different conditions attached to their SIM cards.

if its the older iphone models to the 3gs you can use a prepaid sim just pay for airtime

It doesn't look as though that phone is a prepaid model. It is a Sprint phone and Sprint does it's prepaid options through Boost and Virgin Mobile. Though you may be able to purchase a pre-paid SIM through one of these companies, you will most likely have to inquire directly with them on that.
Hope this helps!
-Kevin

if you are using a sim card from a prepaid phone just bought, and then add it to another att branded phone, it will not work. if you use the sim card in the new prepaid phone, it will work. att locks the sims from working in other phones for 3 months from the factory. i did the same thing with a prepaid phone and a Q9, put the sim in the q9 and it said, no service. put the sim in the prepaid phone, it worked fine. my suggestion is to talk nice ot the att store employee, and they will give you a new sim.

let me know if your phone is doing something different.

Easiest thing is to contact att, tell them you are traveling outside the country for a month, and need your phone unlocked so you can use one of the cheap prepaid SIM cards that you can buy where you are traveling to. If they don't do it, wait 10 minutes, and try again, hopefully getting a different, more helpful operator.

- gohh buy a new battery and put it on a prepaid account and or you might possibly need a new sim card .