Thailand's telephone numbering plan in Thailand is managed by the National Broadcasting and Telecommunications Commission (NBTC) in accordance with International Telecommunications Union's (ITU) recommendation E.164.
Geographic (fixed line) area codes are, excluding the STD prefix 0, one digit in Bangkok and nearby provinces (area code 2) and two digits in provinces (area codes 3x, 4x, 5x, and 7x). In Thailand, an area code is usually shared by several provinces and roughly follows provincial borders.
Fixed-line subscriber numbers are six digits in Thailand (except Bangkok, Nonthaburi, Pathum Thani, and Samut Prakan, i.e., area code 2). Prior to 1980, subscriber numbers were six digits in Bangkok, Nonthaburi, Pathum Thani, and Samut Prakan. In 1980, subscriber numbers in these areas were expanded to seven digits in phases to meet new demands. The first digit of a subscriber number is associated with a specific locale within the area code. In Bangkok, Nonthaburi, Pathum Thani, and Samut Prakan, the second digit of a subscriber number identifies the service provider, which is almost always Telephone Organization of Thailand (TOT), as TOT holds a near-monopoly of the Thai fixed-line market.
Thus, a full national number is 9 digits, including the STD prefix 0. When writing a telephone number with the area code, the area code and subscriber number are separated by a hyphen, also in the middle of subscriber number. Examples:A number 2134567 in Bangkok: 02-2134567
A number 213456 in Nakhon Ratchasima: 044-213456
Thailand switched to a closed dialing plan in 2001, which means that calling within the area code requires the area code to be dialed. E.g., When calling a number 2134567 in Bangkok (02) from a fixed-line phone:Within Bangkok, Nonthaburi, Pathum Thani, and Samut Prakan: 02-2134567
Outside Bangkok, Nonthaburi, Pathum Thani, and Samut Prakan: 02-2134567
Outside Thailand: +66-2-2134567 (the initial 0 of the area code is omitted)
Mobile phone codes are in area codes 8 and 9, and VoIP are in the area code 6, ranging 2 digits excluding the leading zero.
Originally, each mobile phone operator was issued one mobile phone code. Through a series of mergers, there are currently three major mobile phone operators: AIS, True and DTAC. As existing numbers begin to run out, the three mobile phone operators are assigned numbers in code 081, distinguished by the first digit of the subscriber number.
A mobile phone number consist of a mobile phone code and a seven-digit subscriber number. Therefore, a mobile phone number is written as 08x-xxxxxxx.
Mobile phones in Thailand use 900/1800 MHz for GSM. Domestic roaming service is available free within Thailand in places where there is only a single transmitter in place due to restrictions.
As codes are being exhausted, a new range, 09x is made available for assignment. Despite the length of the code, subscriber numbers are seven digits, resulting in a 10-digit national number including the leading zero. Starting 28 April 2011, the prefix 090 followed by 7 digits would be available for use.
Recently, the MICT announced mobile number portability (MNP) service for mobile carriers. Thus, subscribers are allowed to retain their mobile numbers when they switch to another service provider, in a bid to increase market competition. Therefore, the mobile number prefix only indicates the original service provider.
Number portability has not been offered for fixed lines, as TOT holds a monopoly except in Bangkok and some areas in the Bangkok Metropolitan Area.