Most likely the phone won't be useable in Thailand. The U.S. uses different radio frequency bands than the rest of the world. For your phone to work overseas it must be "quad-band" capable. Most phones sold in the U.S. are not. Check the specifications of your model on your service providers or Motorolas websites, the info should be there.

If the phone is locked it will only operate with a SIM card from the one service provider. It must be unlocked to use a SIM card from a different network operator.

If you get a local SIM in Thailand you will also have a local phone number. If you use your U.S. prepaid SIM, then people can reach you by dialing your U.S. phone number. Depending on why you are going to Thailand this can be good or bad...

So, does this trip have anything to do with the two million dollar question of a few weeks back.