When you punch "0", the phone thinks you are dialing a "+" which for US numbers means exit country code "001" (USA has to be number "1" in everything) because there is no + key, zero is coded to do that. I don't do international calling, so I don't know if there is a setting in the phone settings where you can alter this behavior. Only thing I might suggest at this point is to edit your contact when you add it and delete out the 1.
I forgot to mention this happens primarily when using the phone contact list. I do slowly add +66 to the numbers but it is annoying! 🙂 I just looked at the contacts and there is no settings for dialing etc. I can't find a separate dialer app just the phone app that has no settings for that.
As I am using the google contacts I guess I could search the whole database and then change it on the PC 😞
Took a little longer than expected, but I found what you are looking for. From your homescreen, press menu> settings> call. Depending on what mode your phone is in (I'm assuming yours is global), you will have either GSM settings or CDMA settings. This is where you will find the country settings.
thanks in GSM I couldn't see anything like that but I "think" the solution
for me was in Call, then I turned off Assisted Dialing and voila
thanks for all your efforts!