After the country code, a Singapore number has eight digits, a Thai landline eight and a Thai mobile nine, a Malaysian mobile nine or ten, and an Indonesian mobile as many as its operator chooses, up to the 13-digit national limit. We read each regulator's numbering plan, or its latest filing with the International Telecommunication Union (ITU), for all eleven ASEAN members. The ITU's copies are often old: Indonesia and the Philippines last filed in 2006, Cambodia in 2009 and Laos in 2011.
Timor-Leste became ASEAN's eleventh member on 26 October 2025, its government announced, so a form that lists ten countries is a year out of date. A format check, ours included, can say whether a number is shaped right for its plan; it cannot say whether anyone answers it.
A leading zero marks a domestic call in most of the region
Most plans in the region reserve a leading 0 for calls inside the country, dropped after the country code. Malaysia's plan says plainly that "The Access Code for trunk access is the digit '0'", and Thailand's and Vietnam's count their numbers with the 0 included. Singapore has none: its national numbering plan says "the area or trunk codes are not used" in "a uniform 8-digit numbering plan". Brunei's 2014 filing shows only seven-digit numbers after +673 and no trunk prefix, and Timor-Leste's 2013 filing, seven-digit fixed and eight-digit mobile numbers, shows none either; for both, that is our reading of the filing rather than a stated rule.
Singapore's plan also sets aside numbers beginning 3 for internet telephony and data-only services, and says that before the eight-digit format runs out it will move to nine digits, with no date. Laos lengthened its mobile numbers from seven subscriber digits to eight on 1 June 2010.
The prefix 011 marks Malaysia's longer mobile numbers
Malaysian mobile numbers begin 01 and a third digit. Most carry seven digits after that, so nine digits after +60. In a notice of 1 October 2010, the regulator MCMC opened a new prefix, 011, followed by an eight-digit number, from 15 December 2010, and said the existing prefixes 010, 012, 013, 014, 016, 017, 018 and 019 would keep their seven-digit subscriber numbers. The current Numbering and Electronic Addressing Plan allows eight-digit subscriber numbers more generally, so ten digits after +60 is not unique to 011.
The same plan provides for mobile number portability, "the ability for an end-user to change from one Public Cellular Service provider to another … whilst retaining the said mobile number". A prefix shows which block a number was issued from, not which network it is on today.
A leading 2 points to a Vietnamese landline
Vietnam renumbered twice in two years. Its landline area codes changed in three phases in 2017, finishing in August; Hanoi went from 4 to 24 and Ho Chi Minh City from 8 to 28 on 17 June 2017, so that every landline area code now begins with 2. Then, from 15 September 2018, about 60 million 11-digit mobile numbers, counting the 0, were cut to 10 digits under a ministry decision, with the switch completed by 30 June 2019.
When Vietnam merged its 63 provinces into 34 on 1 July 2025, ministry guidance let the merged provinces keep their old area codes side by side until a further notice; we found none. So a Vietnamese landline number written before the merger still has a valid code.
The digit 7 identifies a southern Thai landline
Thailand's filing with the ITU lists fixed area codes from 70 to 79 for the southern region, with 73 to 77 in use, among them 76 for Phuket and Phang-nga and 74 for Songkhla, Phatthalung and Satun. Fixed numbers are eight digits after +66, mobile and VoIP numbers nine.
Fixed lines were due to move to ten digits counting the 0. That change was postponed from 2021 to 2025, and the numbering plan in force from 12 March 2024 put it off again: providers are to add the extra digit within two years "only when the supply of fixed line or mobile numbers is considered to be insufficient". The same filing lists 60 and 89 as non-geographic numbers for VoIP, though both look like mobile prefixes.
The verdicts of our own validator now follow the regulators' plans
We built 69 test numbers from clauses in the regulators' plans and ran them through our ASEAN phone number validator. Until 2 October 2026 it got 36 right. It covered six of the eleven members, and it rejected every landline in southern Thailand and in Indonesia's Maluku–Papua region, along with any Singapore number beginning 65 typed with Singapore selected. Our own phone parser, built on a JavaScript version of Google's open-source phone-number library, got 65 of the same 69, so the site's two phone tools could disagree about one number. The validator now runs on that library, corrects it where a regulator's plan says otherwise, covers all eleven members, and says for each answer how far its plan was checked.
The area digit 9 stands for Maluku and Papua
Indonesia's numbering plan of 2018, Permenkominfo 14/2018, gives fixed numbers ten digits after the country code, an area code of two or three digits and a subscriber number of eight or seven, with eleven digits allowed in areas it calls critical. Area codes begin with 2, 3, 4, 5, 6, 7 or 9; the digits 1 and 8 are not used. Codes beginning with 9 are for the region the plan calls "Wilayah Penomoran Maluku, Papua", which includes Ambon.
For mobiles, the plan fixes a three-digit network code in the block beginning 8 and leaves the length of the rest to each operator, "baik mengenai panjang nomor (jumlah digit)", within the 13-digit limit for a national number. A range such as "9 to 12 digits" seen on reference pages is a library's description, not the regulator's.
A Malaysian toll-free number takes a mobile's shape after +60
Malaysia's plan designates 1300 and 1800 for toll-free and freephone services, in the form 1300 AB XXXX and 1800 AB XXXX. Written after +60, each is ten digits beginning with 1, the same length and opening digit as a ten-digit mobile number such as one on 011, and 13 and 18 are also the start of mobile prefixes. What tells them apart is the two zeros: the plan never lets a mobile subscriber number begin with 0, so 1300 and 1800 cannot be mobiles.
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