Cellular Service with Internet

The main mobile players are AIS DTAC and True. CAT and TOT also dabble in the mobile market but are really more fixed line/cable/WIFI ISP's. 

As for a great Internet package, good question!

In my opinion there is no great mobile Internet in Thailand. 3G(the Thai version) is OK in the big cities but outside it reverts to EDGE.

Proper 3G has recently been launched after protracted wrangling over licences but is very limited in coverage at the moment. I even read today they are now talking 4G:-)

Personally I have an unlimited mobile internet/phone package with DTAC for when I am out and about(I Use iPhone 4) at 300 Baht a month and a CAT WIFI setup at home for Internet. That costs 700 Baht a month. CAT is not the cheapeat but I like their CAT-HINET set up which beams the signal from a tower to a reciever on my home, my average speeds are 10mb/1mb.

Now 3G is TRUEMOVE H and AIS and DTAC

I think for me True company simcard could be better,,because 999 baht you can have unlimited 3G internet and free WiFi @ true WiFi,,,, then you have a 500 minutes free call and 300 sms only in Thailand,,,,, I use this one because example; I need to use message and call everyday so I can save,,,, because if I refill everyday 30baht for call and sms 900baht a month also,, too much save for me,,you can go in some True shop and apply,, go now,,goodluck!!!!)