Hello. I have already tested my Happy Dtac prepaid Sim while in the USA and when the number is called it will ring. What I am wondering is what kind of charges I will run for accepting calls while in the USA on my Thai Dtac Happy prepaid Sim card. I have not signed up for any specific services/roaming.

So doing a bit of googling i came across "Happy Go Inter"... it says that you must enroll in it. I haven't yet when I test call my happy Sim it rings and i can check my balance. am i auto-enrolled in it? am i enrolled in something else? what does it cost to enroll?

http://www.happy.co.th/index.php?option=com_content&view=article&id=295&Itemid=154〈=en

I think international roaming, Happy Go Inter Service, with DTAC/Happy pre-paid is enabled by default. I did not apply for it, but it is enabled on my SIM. You can disable it using the Happy eServices platform.

There is some pricing look-up here... http://www.dtac.co.th/2009/eng/services/roaming_abroad/rate.php

In the U.S., 45 baht/min for a call within the U.S., 90 baht/min to call Thailand, 95 baht/min to call other countries, 44 baht/min for an incoming call and 12 baht per SMS.

If you have to monitor calls maybe best to get a 2nd phone, and a T-Mo or AT&T pre-paid SIM, and calling card, and use that to return calls/SMSes.

FWIW, I plugged my DTAC SIM back into my phone transiting NRT last week and got network from Softbank, I did not even try it when in the U.S. My T-Mo pre-paid SIM also roamed in Japan, and 77 other countries now, but not Thailand.

Happy Go Inter prepaid is enabled by default.

For example in UK it costs approx 70 Bt to make calls and 55 Bt to receive.

12 Bt to send an SMS but free to receive.