Will be traveling with family to Malaysia and Singpore for a week. We will bring a couple of mobile phones to keep in touch in case we split up when traveling, but otherwise don't plan heavy use. I have a plan with AIS on my GNET, other phone is some Nokia using 1 2 Go cards. Are the charges when using mobiles in Malaysia ridiculously high? Would it be better to purchase a phone card there? Compatibility issues? Do my phones need to be unlocked? So many questions, obviously not too conversant with this technology. At any rate, if anyone has any helpful advice it will be much appreciated.

You can buy sim card in Malaysia - celcom is good choice,you can use it for international outgoing calls and broadband mobile,they are cheap,so you can even buy two!

Same about Singapore - Singtel or StarHub,but for mobile broadband you need special sim card,not to be used for voice calls.How cheap? - 80-150 baht.

Thai cards may work in roaming,but usually you need to activate them to roam(call their CallingCentre to do it),I think Thai sim can not send sms in roaming,but they can receive them(free);

receiving calls on roaming cost much money,making calls on roaming cost even more.

Prices aren't ridiculously high for international roaming if using the phones just to stay in contact if separated abroad for short periods of time. I would just use roaming myself if only staying a week.

What do you foresee as your calling requirements? Intra-Malaysia, when there, Intra-Singapore, when there? Any data requirements?

Your Thai SIMs can be enabled for roaming but you might end up paying ~ 80 THB/min. You can both send and receive SMSes, but will pay for both, ~ 10 THB/SMS.

Generally speaking it is usually best to get a local SIM. In Singapore I use M1. In Malaysia I use DiGi.

Thank you to everyone taking the time to reply. It looks like the SIM card option will be the way to go for us.