[Tusanoc]

All major hotels and most guesthouses offer international dialling services but will add a surcharge of 30-40 percent. Business centres in small towns offer fax and phone services which are accompanied by high surcharges.

Bangkok Central Post Office on Charoen Krung (New) Road and some major post offices around the country have a CAT centre which can arrange reverse-charge and credit card calls. In Bangkok these are open from 7 a.m. to midnight, with reduced hours in the provinces.

To dial directly from a hotel room, either contact reception, or dial 001 (for an international line) followed by the country code and telephone number. Alternatively, dial the international operator on 100. Fullrates are charged from 7 a.m. to 9 p.m., with a 30 percent discount between midnight and 5 a.m., and 20 percent discount at other times.

Blue and yellow international payphones can be found on the street, in shopping malls and in airports. These take some credit cards and Lenso phonecards which are sold in the post office and by agents displaying the Lenso logo.

http://www.thailandguidebook.com/telephone.html