I am heading to Thailand for a few weeks and taking my Samsung Galaxy S4 (4g/LTE Device).
Who is the largest network in Thailand? I am looking for the greatest coverage and network speeds – basically the Telstra equivalent of Thailand. Cost is not a concern
I use DTAC every time I'm in Thailand, they have never missed a beat for all the places I went to (various parts of both central and southern Thailand).
From memory, they are the cheapest if you want the most data access.
Just to followup post trip….
DTAC (Happy SIM) was the best for 7 days unlimited 3G - cost 299baht (AUD$10).
Didn't come across any 4G at all over there, even in Bangkok.
AIS is might the one you looking for, they are like Telstra over there.
Best way is to get it at the Airport after you got your luggage.
http://en.wikipedia.org/wiki/List_of_mobile_network_operator…
When I was there for 6 months I pretty much tried them all. AIS and DTAC were the cheapest but very poor 3G/4G service, stupid pay for sms being sent by default that you have to opt out of and more nasties - but they had the best rural 2g service which is important (AIS being better than DTAC).
I also had an AIS 3G mobile broadband usb stick which worked great in Bangkok but didn't try it outside of there.
Truemove was by far the best for 3G/4G when in the usual areas, but had pretty shoddy 2g service when in the sticks.
This was 2011-2012 though, things may have changed, but I recommend getting an AIS and Truemove sim.
YMMV though.