As the Original Poster, let me update the original message and ask more questions. Note: I have no experience with cellphones with SIM cards, so please forgive if these questions seem somewhat simple:

1. I received two AT&T Moto V600 quad-band GSM phones from my brother, who upgraded to newer models. Sent them off for unlocking, and received them back yesterday. (I didn't see seanthepilot's recommendation to have the unlocking done in BKK until too late, but it was only $10 each here.) I will use one and my daughter one while we visit BKK (and maybe during a brief trip to Cambodia).

2. When I purchase a SIM card for each phone in Bangkok at the end of August, will the phones then have local (BKK) phone numbers? Can someone recommend a brand of SIM card that will be without hidden or excessive charges?

3. When we travel over to Siem Reap, any phone recommendations? We will be there for 3 days, then back to BKK.

4. I will be returning via Shanghai. If I have time left on the BKK SIM, I expect to use it up calling internationally from there. I assume the phone will work there.

Thank you!