Calling Cambodia from the United States explained:

• 011 - US exit code; dial first for international calls made from the USA or Canada
• 855 - Country Code for Cambodia
• Phone Number (may not begin with 0):
  • fixed - mostly 8 digit and some 9 digit numbers, area code included
  • cell phones - 8 digits; newer cell numbers are 9 digit
• sample call from US to a landline in Phnom Penh: 011 855 23 ??? ???

How to dial to Cambodia cellular:

• dialing format for calls to a cell phone: 011 855 XX ??? ???(?)
• XX can be: 1X, 68, 69, 70, 76, 77, 8X, 9X (this list may be incomplete)

Area Codes:

Phone Books:

• Official Cambodian Yellow Pages
• Canbypublications.com - a comprehensive guide to Cambodia