SIM Cards, Phone Companies, and Signals
When you first arrive in Thailand, it is recommended you pick up a SIM card at the airport, where they are geared for newcomers. There are 3 main mobile companies -- AIS, True, and DTAC. There's not a huge difference between them. (In the past, I used True for phones staying in Bangkok, AIS for traveling upcountry, and DTAC I wasn't sure about, but the service differences seem to me to have narrowed a lot over the years.) There are some other phone companies but they are very much in the minority.
You must present your passport (or Thai ID card) and register your phone number. There are no anonymous SIM cards.
You might later change your phone company once you settle into a particular place to stay, especially if you live in a suburb or upcountry. This is because there might be a cell tower of a particular phone company which gives you a better signal than the other companies. Upcountry, you might even get a signal from only one company. The best thing to do is ask around to find out what other people use. You can keep your phone number but switch it to another provider, but after you order that it typically takes days to a week to be executed. If you haven't given out your phone number to a lot of people, it might be better to just switch to a new SIM card and phone number from your favored company.
It's a good thing that many phones allow 2 SIM cards. While many people use that for their domestic and overseas numbers, we use it for times in which one carrier has a significantly weak signal.
My wife and I have phones on all 3 companies, whereby it's interesting to see the differences in signal, and sometimes we call people back on a different phone number for a better connection.
Thailand has a lot of cement structures, and cement attenuates signals much worse than wood homes. (Wood places tend to not last as long in the tropics. Also, since Thailand has lots of cheap cement but more expensive metal, more cement is chosen.) In townhouse/shophouse rows or other crowded places, the cell tower might be at a bad angle, requiring the signal to pass thru a lot of walls, whereby you must step outside for relief if you don't have multiple SIM cards to choose a better connection.
In Thailand, all domestic calls are dialed starting with a 0, and then the second digit is always a non-zero. (Some people may think this is obvious because it's an international convention, but actually, there are still countries where domestic numbers still don't start with a 0, such as in the USA.)
All telephone numbers in Thailand are 10-digit for mobile phones and 9-digit for wired landlines, except some special emergency 3-digit numbers, and some commercial 4-digit numbers like when dialing for food delivery.
09-1234-5678 for a mobile phone (or if you have other hyphen preferences, 0912345678 or 091-234-5678)
Mobile phones start with 09, 08, or 06.
If you are outside Thailand and dialing into Thailand, then you drop the leading zero, and add a +66. For example, to call my office inside Thailand, you call 02-255-0620, but to call it from overseas you call +66-2-255-0620. (Instead of the + you may need to put your country's international direct dial prefix, such as 00 for some countries.)
Occasionally, you may see old signs with fewer digits. When I first arrived in 1994, some phone numbers could be dialed from some places with as few as 6 digits. As mobile phones hit the market, and also landline networks expanded, the standard for the number of digits increased, and digits were added.
In Thailand, only the caller pays. There is no charge for receiving calls, only for making calls.
Hardly anybody uses a landline any longer, but be forewarned that calling a mobile phone from a landline such as an office phone may cost 3 baht per minute! So always call mobile phones from other mobile phones. Some very old billing conventions are still in place. You would be insane to make an international phone call from a landline. Just stick to mobile phones and internet calls.
Roaming and Foreign Phones
Foreigners often bring their foreign phone into Thailand on an international roaming plan. Often, their internet and other performance isn't vary good. Local SIM cards normally perform much better. If you have a phone which takes 2 SIM cards, then you may want to make your foreign SIM card to be your second SIM card and put in a good Thai SIM card for internet connection.
For local people to call you, they may be reluctant to call your foreign number or might have difficulty in doing so if their phone is not enabled for overseas calls because they normally don't make them and have a fixed fee prepaid package with doesn't include international calls, or something like that.
You can also get international roaming on your Thai SIM card and account, but of course it's relatively expensive.
Mobile Phone Companies
There are three main mobile phone companies which can operate in Thailand (i.e., have been granted a "concession" by the Communications Authority of Thailand):
There was a plan set in place to merge True and DTAC in late 2021 but there have also been objections by AIS and others in 2022, so we shall see whether or not that goes thru.
The relative performances of the three companies have varied widely over the years. I will try not to bother readers too much with the history high up in this article, and actually I've largely deleted a lot of history from this page, but in short, Thai companies started mobile phone service here rather than it being started by foreign companies, and mobile phone usage was adopted in Thailand much more quickly than in many more modern overseas countries, partly because the government landline service was so bad so that Thais looked to mobile phones as an alternative, especially businesses. When I was here in 1994, many offices I consulted to relied on mobile phones inside the office instead when their landline calls didn't get thru.
Then foreign companies came in and bought up huge shares of these companies, bringing investment and technical know how as technologies evolved. There's been a lot of selling and buying, which has caused disruptions, variations in relative performance, and differences in rates of adoption of faster standards. Of course, the numbers of new cell towers also affect coverage. AIS initially had the best nationwide coverage, whereas True initially focused more on urban centers, for example.
I've seen service degrade with particular suppliers from time to time, such as when there is a sell and buy disruption, a super cheap promotion to lure users from other companies and get new users which overloads a network, and other glitches. However, performance seems more steady in recent years.
AIS was the company founded around 1990 by the now exiled ex-Prime Minister, Dr. Thaksin Shinawatra, who was overthrown by a coup in September 2006. At the time, his was one of the first two quasi-monopoly companies which received a government concession, and the DTAC predecessor followed later. AIS did well but its initial competitor faltered. In the 1990s, AIS and DTAC competed closely, but the quality of service of AIS overall was usually significantly better than DTAC. There are also the allegations (including in court) that AIS benefited from preferential government concession rates ...
Thaksin sold his company to the Singapore telecom conglomerate Temasek in early 2006 when at the peak of his power (tax free, and in alleged violation of some laws), before he was ousted by the military, and complications in regard to that sale were part of the problem. Further, there are some legal problems about that sale, especially restrictions on foreigner ownership of a domestic telecoms company. It appears Temasek believed Thaksin's hold on power in Thailand was permanent, as he had gotten away with abusing his power before, his party and an overwhelming absolute majority in parliament, he had a strong base of voter support in upcountry rural areas as a populist, and was so extremely wealthy ... but everything changed with the surprising military coup ... so Temasek and the gang had to deal with some difficulties, to say the least ...
... and after that, with all the sudden uncertainties about what would happen to AIS, there was a lot of gossip about financial neglect and other changes which affected AIS significantly.
AIS performance and service, which was excellent up to that point, dropped severely for years, though it eventually bounced back and is now my favorite company again, but there were some years when it was abhorrent.
I also went thru a roller coaster ride with DTAC, and saw the rise of True.
Some more details of history:
AIS was the first mobile phone company. It was started back in the early 1990s, as one of Dr. Thaksin Shinawatra's companies, long before he entered politics. AIS was started long before mobile phones became trendy, and was an expensive and major financial risk at the time. Dr. Shinawatra was ahead of his time, as usual. He was eventually Prime Minister, then overthrown by a military coup, then the leader of the "red shirts" who came down from upcountry to Bangkok in convoys and mounted big street protests.
His main competitor in the early 1990s was a guy and wannabe friend named Sondhi, but their relationship got very sour. Sondhi became a sore loser, though Thaksin's business tactics were rather cut-throat and mercenary. Sondhi would later lead the "yellow shirt" protesters in opposition to the "red shirts", after 2006.
After mobile phones caught on and became a trend in the early to mid 1990s, DTAC entered the market around 1996 (I don't know the exact year you can pin their significant ramp up to).
DTAC complained about government favoritism because AIS doesn't pay as much of a tariff to the government, due to its pre-existing contracts negotiated with the two government monopolies -- the Communications Authority of Thailand (CAT) and the Telephone Organization of Thailand (ToT). These were negotiated long before Dr. Thaksin entered politics. In a well known court case, this tariff descrepancy was upheld, partly because it was negotiated before DTAC entered the scene.
I don't see this as a corruption case. AIS entered the mobile phone business before it was trendy, and indeed struggled financially for years because mobile phones were not trendy at the time. AIS paid the price of taking risks, and deserves the profits -- it's better to support pioneering entrepreneurs than copycats.
The networks are connected, so DTAC initially benefited from AIS's expensively established nationwide antenna system, to place and receive calls from AIS users.
Furthermore, I have usually been impressed with the quality of service of Dr. Shinawatra's companies, and those of his wife, compared to much of the competition. There are some fundamental reasons Dr. Thaksin Shinawatra and his business minded and modest wife are highly successful in society. The management and personnel of these companies have clearly been chosen carefully, and the leadership exemplary.
True essentially broke out after the year 2000, formerly under the name Orange (with French origins and foreign investment), initially in a joint venture with Telecom Asia (TA), but not under the name True. (Notably, I consulted with an engineering operation involved in deciding upon antenna sites and designing the antennas to be built, back when it was Orange coming to Thailand.) Later, out of parts of the TA Orange group, a new company called True emerged, which is well known for its broadband services and rapid growth, as if plans were made which many people thought might turn out to be too good to be True. It was a bold and forward looking brand name, True. They had bold ambitions heading into the future.
Hutchison was around since the 1990s when pagers were an economical alternative to mobile phones, and Hutchison had some unique and cool features for their mobiles, but Hutchison faltered and didn't invest enough as a competitor as regards mobile phones.
CAT has also dabbled a little.
This page was updated in early 2022, so if you're reading it much later than that, some things might be a little out of date.
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