Here's a quick algorithm that will save you a lot of money:
1. Download the True Thailand app (it's the most popular local mobile operator)
2. Go to a local store that sells food and other small items (7/11 and other chains won't work). You'll need to walk around and look for them or ask locals. Or find a mobile operator office; they exist.
3. Explain to the seller that you only want a Dtac SIM card (True and Dtac are the same mobile operator). It costs 50 baht or 125 rubles.
4. Activate it with the seller on the spot (you'll need your passport).
5. Now you have a phone number -> register in the app using it.
6. I immediately received a gift of 3 gigabytes of free data. That's enough for a short vacation. (This happened on December 28, 2025)
7. If your gift didn't arrive or you need more data, you can purchase a data package through the app. If your gift didn't arrive, meaning you don't have an internet connection to access the app, you can buy it via WiFi at your hotel. In any case, the data packages in the app are cheaper and come in more varieties. You can pay for the package with any foreign bank card.

Now, some background.
I arrived in Thailand at the end of 2025, and it wasn't my first time, so I'm familiar with prices. And when I went into a 7-Van and found out the cost of a SIM card, I was absolutely stunned. I know three mobile operators: True, Dtac, and Ais. The first two are more common. You can buy a SIM card at the airport or at 7/11—everyone will tell you that. But they cost 600-700 baht (1,500-1,750 rubles). You'll agree, that's a big difference compared to the 50 baht (10 times cheaper) in my story. Polite salespeople will pretend to be trying to help you, asking how long you're staying and how much internet you use. Don't fall for it! Go for a walk around the city, find a place where you can just buy a SIM card, and use the money you save to go out for a tasty meal or take a trip somewhere interesting.

The method described is what locals use in Thailand, meaning it's all easy and quick, but no one will tell you about it because you're a tourist.

Good luck on your vacation or trip!

Location: Thailand