Looking for some good advice, what plan should I pick for running WhatsApp, ICQ on a smartphone? No browsing and leeching.

Based on traffic and not time/high-volume downloads.

Just got 1-2-Call out of the box, seems that it will eat my balance pretty soon =)

I-Kool 3G. New sim for 99 baht comes with 500Mb data and only need to top up 50 baht a month to keep active. Or get a TrueMove sim and they have a 50Mb plan for 50 baht a month. It does not auto-renew so you have to re-order it every month. If you want to use you 1-2-Call sim the cheapest data plan is 150 baht a month. You need a volume plan as smartphones are connected to the data 24/7 and if you pay by the minute that is 60 baht per hour. Volume plans can stay connected all day and only charge for data traffic. That is what you need for a smartphone.

Depends on the smartphone. I know that for example keeping notifications on on an iPhone will eat your minutes in real time. It constantly checks for notifications (how that doesn't totally destroy the battery is a mystery BTW).

So on an iPhone, you have to turn off: Notifications, Location Services, and Automatic Email checking, then a time based plan should be OK.

On other smartphones, I don't know, but I assume they work in similar ways. Only BB should be better as BB is using service messages to poll for email so it shouldn't use data (I believe - not 100% sure on that either). And it doesn't even have a generic notifications framework

Nokia "smart phones" should be fine too as they hardly do anything