Area Code 42 – Loei/Mukdahan/Nakhon Phanom/Nong Khai/Sakon Nakhon/Udon Thani

Geographic Coverage and Administrative Jurisdiction

The Thai national destination code +66 42 is a geographic area code assigned to the upper northeastern region of Thailand (Isan). It serves the provinces of Loei, Mukdahan, Nakhon Phanom, Nong Khai, Sakon Nakhon, and Udon Thani. These provinces are administered under the Thai administrative divisions, each with its own provincial government. The code covers both urban centers and rural districts within these provinces, including the cities of Udon Thani, Sakon Nakhon, Nong Khai, and the border town of Mukdahan, which serves as a key gateway to Laos.

Dialing Formats and Caller Instructions

For international callers, the number must be dialed as +66 42 XXX XXX (or 0066 42 XXX XXX from countries using international prefix 00). The total number length after the country code is 8 digits, with the area code '42' followed by a 6-digit subscriber number. When calling domestically within Thailand from another area code, dial 0 42 XXX XXX (trunk prefix '0' + area code '42' + subscriber number). For local calls within the same area code, the trunk prefix and area code may be omitted, but it is always safe to dial the full domestic format.

Numbering and Overlay Considerations

Thailand's numbering plan follows ITU-T E.164. The '42' code is a geographic code, and there is no overlay code in this region; the area code remains mandatory for calls from outside the region. Subscriber numbers are fixed at 6 digits, and the total national significant number (NSS) is 9 digits (including the leading '0'). The code is administered by the National Broadcasting and Telecommunications Commission (NBTC) of Thailand.

Services and Usage

This code is used for fixed-line PSTN services, including traditional analog lines, ISDN, and increasingly VoIP-based fixed services that retain geographic numbering. Businesses and residences in these provinces use this code for local telephony. The region is less densely populated than Bangkok, but it includes important commercial and administrative hubs. For example, a fixed-line number in Udon Thani might be +66 42 123 456. When calling from abroad, ensure you replace the leading '0' with the country code '+66'.

Important Notes for Callers

Always verify the subscriber number length, as some numbers may have been migrated or ported. Mobile numbers in Thailand begin with '06', '08', or '09' and are non-geographic; they are not part of this code. For international callers, using the + sign is recommended for compatibility with mobile networks. If you encounter difficulties, check with your carrier for international dialing instructions.