Planning a 8-10 weeks trip to S-pore, Sabah and later to Bali. Is there an "all s-e asian" operator that have a pay simmcard covering these areas. Would like to pick one up in S-pore on the way in for use for the whole trip. Preferably with possibillities to make international calls aswell. Found on an earlier trip that I could use the locally bought thai (1-2 call maybe) paycard for calls to europe whitout any hassles.
Is there something useful to be bought i S-pore?

There is no single SE Asian operator but many places offer 'international' SIM which can be useful. These international SIMs provides a low-medium cost plan (cheaper than roaming) plus many offers free incoming call feature.
Know nothing about these guys but it may be what you need?
http://www.ausbt.com.au/new-sim-card-offers-unlimited-data-roaming-in-asia
https://www.bridgealliance.com/datasim.aspx
Good luck!
You can buy a local Sim in most SEA countries for about $5 ($10ish in a few) and you get enough talk time included to cover most tourist trips. I usually give mine away as I'm heading for the airport/border if there is talk time left.

Calls will be cheapest if buying a new pre-pay sim card in each country. You can keep your native sim for receiving calls from home, and make calls on the local sim.
A dual sim phone like the Nokia C2-00 is useful.
Yes, a local SIM for each country is the way to go. Step across a border and you'll immediately notice the change in call costs.
Beware of the terms of service. Eg, you may be able to buy a SIM for app. US$5, but after a certain amount of days you may be required to buy a minimum amount of pre-paid time to maintain it. I've used a Malaysian company that required 1RM per day, to be purchased a month at a time, it was cheaper for me to buy a new 10RM SIM which was good for a month.
If you're in a place where they take your info when you buy a SIM (like Malaysia) giving the chip away is not a good idea.