This is a very small question, but at least it has a definite answer. I’m in America, and I have a Thai cell phone number I need to call. It begins with (or I was told it begins with) 081. The cell phone was bought in Bangkok but the person himself is in Rayong. I tried calling the obvious (001 66 081 . . .) but I was told I didn’t need the zero in the 081. When I left it off, I got a wrong number. Any ideas, or should I just wait until he checks his e-mail?
The zero is used only within Thailand. From outside Thailand, you use the country code, which is 66. So the number, after whatever you dial to get outside of the US, should be 6681-xxx-xxxx. There will be seven numbers following the 6681. It won’t matter where the person is or where the phone came from; that number will work anywhere. I can confirm that that is indeed a cellphone number, because of the position of the 1; in that position, 1 and a couple of other numbers signifies cellphone.
If it’s still a wrong number, that means the person screwed up and gave it to you incorrectly.
Hope this helps! 
Try 011 66 81 xxxx, not 001 66 81 xxxxx. The International Direct Dialing number (IDD) from America to another country is 011, not 001. If you’re using a cell phone, you can also dial +66 81 xxxx. On my phone, you make the plus symbol by holding down the 0 for a second or so.
Actually, it’s both the 8 and the 1 that designate a cellphone. All cellphone numbers in Thailand have 8 in that position, followed by 1 or 9. (Also 4 or 6, something like that; just recently added to keep up with growing demand. But 1 or 9 for sure.)