Thailand has excellent, cheap mobile data. The only way to get it wrong is paying your home carrier for it.
Networks and 5G
Roambee uses partner networks AIS and dtac. Bangkok, Chiang Mai and Phuket have broad 5G; the islands are 4G with good speeds near towns and patchy coverage on remote beaches.
The roaming toggle
Your Roambee line must have Data Roaming switched on — it is a travel SIM by design. If you see "No service", that toggle is the first thing to check.
How much data
Ride-hailing, maps, LINE and photos: 400–500 MB a day. A week fits in 3–5 GB; two weeks needs about 6–7 GB, so the 10 GB plan (€17.90) is the safe choice. A month of island-hopping with video calls home wants 20 GB.
Southeast Asia hops
Adding Vietnam, Cambodia or Bali? The Southeast Asia regional plan covers 7 countries on one eSIM: Cambodia, Indonesia, Malaysia, Philippines, Singapore, Thailand and Vietnam.