[General Topics] phongpan355:
If you're travelling to Thailand very soon, and you want to access the internet, keep in mind that there's very few places that allows you to get free wi-fi without any subscriptions or SIM card (like in many shopping complexes that need a SIM card for wi-fi), or you'll need to spend time to register for free wi-fi (especially Suvarnabhumi Airport (BKK - Bangkok) that I see one person registers their wi-fi for ten minutes, but the airport's wi-fi is incredibly fast) so that if you want to use the internet in all places, you'll need a SIM card for that.

And if you want to buy a new SIM card in Thailand, DO NOT believe in their advertisements. In Thailand there's one network that claims that their 4G LTE is fast, but of course they're slow and has very weak signal, and when the signal is weak, and you only have 3G (which is HSPA+), it's only 0.2Mbps - 5Mbps. See below for consideration.

1. True Move H

Don't believe that their 4G LTE and 3G HSPA+ will be fast as you expect. Their signal is very weak and not nationwide, and on 3G it's nationwide, but you'll get slow speeds (although you have very strong signal).

Their tourist SIM is 299 Baht (which is considerably expensive) and you have 1GB internet, which will slow down after being used up.

Their staffs are terrible and I don't have any words to describe, go try at your risk.

You'll need a phone compatible with UMTS/HSPA+ 850MHz/2100MHz and may include LTE 2100MHz. But don't care about this, their network is slow.

2. dtac

Even though their 4G LTE is not very fast compared to other networks, but their 4G LTE is stable and smooth. 3G HSPA+ is faster than 4G LTE so that you'll want to try out. The network is available in most areas with some blackspots, but thanks to their tower-sharing plan with AIS, another network, after confirmation, the signal WILL be better nationwide (but not now). Their 3G HSPA+ is based on the dual-band network like True Move H, but this network (dtac) has more performance.

Their tourist SIM is 299 Baht that's enough for 1.5GB internet (and will slow down after this). There's also 599 Baht for 4GB internet (and also slow down after this).

You'll need a phone compatible with UMTS/HSPA+ 850MHz/2100MHz, GSM 1800MHz DCS, and LTE 2100MHz. I highly recommend this as I have best 3G speed on this network (highest speed was 26Mbps, average is 10-16Mbps) and not on any other networks.

3. AIS

Due to their 3G HSPA+ has only single-band, their network is slow, and they've made more cell towers & small cells in particular areas, BUT as I've told you earlier, AIS had plans to share their towers with dtac, so soon, AIS will have faster network, but I won't recommend you to try since their network is slow (but have high performance equipments).

It's hard to describe anything about their tourist SIM, but you can find info here: http://www.ais.co.th/roaming/visiting/sim-for-traveller-en.aspx

Their network only uses UMTS/HSPA+ 2100MHz, that's why I told you that AIS is slow, and they consist of GSM 900MHz where they'll abandon their service soon.

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NO networks in Thailand that use CDMA (actually there was, but they abandoned since April 2013) so that Verizon & Sprint phones won't work, and AT&T uses different bands, so that T-Mobile and off-contract phones MAY work.

Thanks for reading this thread and have a good day choosing SIMs!