Note: Post below was originally published in year 2013. Today, most people who are using Smartphones (Android and iPhone) can easily enable Thai language in which you can select in your phone’s virtual keypad. However for any reason you are not using Smartphones and prefer the old fashioned phone, then the phone model Nokia Asha would have the Thai consonants and vowels being displayed.
For me, I also bought a laptop in Thailand, purposely for the Thai keyboard. Of course I also checked with the shop if the brand provides international warranty.
Original post:
If you are learning to read and write in Thai, you may want to consider getting a mobile phone a physical keypad with Thai consonants and vowels such as shown below:

The best place to get the phone would be in Thailand itself. If you purchase it online, it would be very expensive. Very.
Of course all Smartphone would come with the Thai language option if you change the language setting to Thai. But if you have a friend whom you can text Thai sentences to, the physical keyboard would be the best.
In my opinion, the most convenient phone to have the Thai physical keyboard is on the Nokia Asha. as it contained the full qwerty physical keyboard similar to a Blackberry Bold.
I bought this Nokia Asha from Mocchit bus station in Bangkok via one of its shops selling mobile phones. The phone cost me 2900 baht and comes with dual SIM.
The first time I saw the phone I really love it. It is now my main phone that I use for caling and sms. When I sms in the simple amd limited Thai language that I know, the phone makes it easy to type in Thai.
By the way, you can also find a number of stalls there selling the so-called iPhones and Samsung for about 1900 baht only. I nearly got tricked at first until I noticed the camera quality was very bad and not clear. For Smartphone, it is not worth buying imitation as the quality would be what we pay for.
But for the Nokia Asha, as far as I can tell it is genuine. The battery lasts for days without charging if on light use.