Calling Thailand from the United States explained:

• 011 - US exit code; dial first for international calls made from the USA or Canada
• 66 - Country Code for Thailand
• Phone Number (may not begin with 0):
  • landlines - 8 digits
  • cell phones - 9 digits, first digit is 8 or 9
• sample call from US to a landline in Bangkok: 011 66 2 ??? ????

How to dial to Thailand cellular:

• dialing format for calls to a cell phone: 011 66 X ???? ????
• X can be either 8 or 9

Starting digits for landlines in largest cities:

• Bangkok: 2
• Chiang Mai: 52, 53
• Chon Buri: 33, 38
• Hat Yai: 74
• Lampang: 54
• Nakhon Ratchasima: 44
• Nonthaburi: 2
• Samut Prakan: 2
• Udon Thani: 42

Phone Books:

• Yellow Pages Thailand
• TOT Phone Book - official people search, in Thai