Can anybody help me out with the following questions. I've had a prepaid DTAC card with a nice number for a while now and I'd like to continue using it... but once I get settled in Bangkok (september, am i ever so lucky re: the 8-prefix thing) I would like to change a few things ...

1. Can I change from prepaid to postpaid without changing to a different number?
   
2. Does DTAC support two SIM cards with the same number? (since I have a pda phone and a tiny phone and don't want to carry the pda phone with me everywhere)
   

Also, does anybody know how expensive roaming abroad with DTAC is?

1. yes - for the exact requirements check with DTAC. You have to go to one of their own outlets, not to some sub agent.

2. not sure, best you check with DTAC hotline (good luck, though....)

roaming is pricy

For question 2, if you have to resort to using two SIM cards (one for each phone), see if you can set up call-forwarding from the PDA phone to your smaller one.