Internet browsing in Thailand, hahaha.
Just take the Nokia. I've been to Thailand 4 times now, and never needed to make a telephone call. If I need to call home, I usually don't and email instead, but its relatively cheap to do so in the hotel.
3G is relatively scarce, depending where you are. Bangkok is fine, but elsewhere you will only get it in certain areas of the city, such as Phuket. It is pretty poor quality anyway. If you're truly on a holiday, you wont need it anyway.
AFAIK, DTAC dont do 3G, not too sure about AIS.