I would like to monitor how much data-traffic I use. How?

Possible Duplicate: Monitor wifi usage? Is there a way to have an alarm warn me every time I spent another 100MB and telling me the total I've spent on the last billing period to avoid going over my limit and into debt in Android?

Is there any way to control how/when the 3G radio goes to sleep? Is that, in fact, what it is doing?

Usually I like to bring my Android phone with me when going abroad. But I use it very carefully because I know that it is very expensive to consume data traffic and roaming fees, when I'm abroad. How do I best use my Android without getting expensive bills when coming home again? Is there any specific settings that I should do? Any good applications or other tips that can be useful when going abroad?