Dialling directly from overseas to a mobile or landline in Thailand is fairly straightforward, but the task can be complicated by the way Thai phone numbers are sometimes listed.
Numbers for hotels and other businesses that frequently deal with international calls often can be dialled just as they are printed on the business's website. Other businesses or private numbers may only list the number as dialled locally.
An easy way to tell the difference is to check the prefix. If the first number is a zero, then it is the local version of the number. To dial it from abroad, simply drop the zero and add the country code (66) and international dialling prefix for your country (1 in the United States).
Dial the international outgoing call prefix, or "exit code" for your country. In the case of the U.S., this is 011. If you do not know the exit code for your country, you can find it online at the How to Call Abroad website (See resources).
On many mobile phones, you can substitute a "+" symbol for the exit code. In this case, enter the "+" symbol as a prefix to the rest of the phone number and your phone will dial the exit code automatically.
Dial the country code. For Thailand, this is "66". So the dialling prefix for the entire country of Thailand, dialled from the United States, would be 011-66 (or +66).
Dial the area code or mobile prefix as listed. This will be either one or two digits. Bangkok's area code is 2. Mobile phones prefixes are usually the area code in which the phone was purchased, preceded by the number 8.
Remember that the local area code is often listed with a zero in front, and this is only for dialling from within Thailand. To call from abroad, drop the zero.
Dial the seven-digit number for the individual phone.
As an example, the phone number for the Tourism Authority of Thailand's Bangkok office is listed locally as, "(02) 250-5500." To dial this number from the U.S., dial the exit code (011 or "+"), followed by Thailand's country code (66), then the area code (don't forget to drop the zero), and the local number. So a caller in the U.S. dialling the Tourism Authority of Thailand would dial 011-66 (2) 250-5500, or +66 (2) 250-5500.