What mobile services allow expats in Thailand to keep their number without monthly fees?

If you know roughly how much data you use, and you want to keep your foreign number, you could use airalo e-sim

With wifi everywhere, mobile data use is generally pretty low now.

I've used my AIS sim for years. Just top up every month and get 80GB data for 300 baht. And if I dont top it just tells me that I didn't get the plan and it waits for me to top up to add the pla automatically.

I think what DTAC and True tried to tell you, is that you need to register your SIM. Just walk into one of their shops with your passport and get it done.

I always just buy a 6 months DTAC non tourist, it's good value. Just go to any non touristy Dtac shop.

DTAC and you can "Buy" days validity. About Bt18 for 180 days.

AIS 2500 baht a year for unlimited data just top up for calls

Have been using my Ais tourist prepaid Sim until now since 2017 no monthly plans just top up to extent validity

Many people don't know that you don't need any active plan or package on your phone to keep the SIM card and SIM number alive. Every time you do a top up of funds for any amount to your prepaid SIM card, it extends the validity by 1 month. So for example, if you top up 20 baht 12 times in a row, your SIM card and phone number's validity is extended by 1 year. There's no recurring charge, and the balance from your top ups just sits in your account waiting to be used. When you come back to Thailand, just open your carrier's app on your phone and select a data/voice package that suits your needs for the period you are in Thailand. The rest of the time, just check the app which shows your remaining topped up balance and your SIM's validity date, and top up small amounts as needed to extend the validity.

I use dtac 1 year unlimited data for 2500b.. cheaper than monthly by far. if your sim expires after 1 year you have 2 months until they cancel it but it's easy to just renew and keep it in use. I had my same number for 7 years. 2500b is nothing for unlimited net at 10mb imo.

AIS tourist sim with a data package has been great for me. 1300 baht for 6 months unlimited data, and it's faster than my home internet most days

With AIS you can top-up the prepaid SIM to get up to a year of validity, each minimum top-up adds 1 month.

I've been with DTAC for the past few years and it's cheaper to pay monthly than to buy an annual plan for me. I mainly text but do watch some social media video shorts so their 30GB/month plans suit me. Speed is good if it's over 10Mbps so i choose a plan that offers 15Mbps for 300THB. The service receives Thai SMSs in Australia though i don't rely on that feature.

I'm using AIS and for now they have annual plans available but only on new sim cards. I paid around 2200 THB for 1 year with 50 GB monthly data.

Note: This has to be bought from AIS shop and not from the kiosks at the Airport.