A great many restaurants, bars, hotels and accommodation complexes offer free Wi-Fi, which is great, but what do you do when you're on the beach and want to post your latest pictures to social media, search Google for that fact that you must know now or find yourself lost and need your maps App to show you the way? Luckily it is relatively easy to obtain a Thai SIM card, and a huge amount cheaper than paying those high data roaming costs, as long as your phone is unlocked to any network. If your phone is not unlocked then it may be beneficial (and cheaper) for you to buy a cheap mobile phone along with a Thai SIM card for use throughout your stay.
The National Broadcasting and Telecommunications Commission (NBTC) of Thailand requires that all SIMs are registered to a user. This means that when you purchase your SIM card the staff will take a photo of your passport and upload it to the NBTC servers from inside their smartphone app.
There are three main Thai mobile network providers: AIS, DTAC and True, all offering Traveller SIM cards and various packages. Prices continually fluctuate but you can expect to pay somewhere around 100 Baht for 7 days of unlimited internet, telephone and text messaging (within Thailand). You can also find 15 and 30-day packages to purchase with prepaid credit, starting at 300 Baht. All three providers are comparable in 4G data speeds and have similar coverage in Thailand's major cities. True is the best value for money, however AIS is the largest operator with the best coverage and DTAC has the best customer service.
With an unlimited data package on your Thai SIM card you should be able to use your Personal Hotspot function (if you have an iPhone) to connect your laptop/tablet/kindle (or any Wi-Fi enabled device) to the internet too, ensuring coverage everywhere.
You can obtain a SIM card as soon as you arrive at Bangkok's Suvarnabhumi Airport - all three network providers have branches in the arrivals hall, just ask your chosen provider to install and set up a prepaid SIM card for you and ensure the data connection is working. Even if you arrive at an unsociable time the chances are these shops will be open.
You can also obtain a Thai SIM card from a 7-11 store, with over 7,000 7-11 stores in Thailand you're bound to come across one very soon in your trip! Most shopping malls will also have official DTAC, AIS and True retails, so finding a place to buy a SIM card is really easy. Just remember to take your passport as they will all ask for ID in order to sell you a Thai SIM card. Ensure that your unlimited data is working before you leave the shop so that you don't eat up your credit straight away! Don't forget to keep your original SIM card somewhere safe!
Once your unlimited package is up you'll need to 'top-up' your credit. You can get daily internet packages (20-80 Baht a day), or unlimited monthly data (starting at 400 Baht a month). There are many different packages available, including call minutes and text messaging/SMS.