Welcome to Thailand SIM Cards! I'm going to tell you the best data plans with prepaid SIM cards by every telcos!
Requirements
After you pick your phone number, give the passport to them and then top up the amount you want. If you're Thai residents, use your ID card to register.
Which one suitable to you?
For those who stay less than 1-2 weeks, get a tourist SIM which costs 299-599THB. All SIM cards include data and credit.
For those who stay more than 2 weeks, want cheaper option or for those who enter to Thailand multiple times, recommended to get regular SIM which costs 49-50THB. All SIM cards include 15THB credit. Top up a bit if you want to buy some internet or calls.
DTAC
Thailand's third leading telco. They also offers unlimited data with internet speed limit.
Dtac offers unlimited data from as low as 15bhat/day and as much as 649bhat/month. Speeds available from 256kbps all the way up to 4mbps.
SIM card can be brought at most telephone shop within Thailand, comes with prepaid SIM card when brought together with Dtac branded phone (bundle) or Dtac Center nationwide. The price range is 49bhat-299bhat++. Tourist SIM also available.
Link: https://www.dtac.co.th/en/prepaid/products/go-no-limit.html
TrueMove
Thailand's leading telco, satellite TV and cable TV operator. They have unlimited data with internet speed limit or limit data with internet speed limit (after reach the quota will slowed down to 64kbps).
SIM card can be brought at most telephone shop within Thailand, True Center, 7-11 or comes with SIM card when brought together with phone (bundle).
Link: http://truemoveh.truecorp.co.th/topping/index_en.html