HTC Magic :: What Apps Are Connecting To The Internet And How Much Data Have They Transferred

I am a new HTC Magic (Vodafone) user and have downloaded a number of useful Apps from the market. Since I work away from the UK (and have roaming disabled) and I have a Wi-Fi at home, I do not have a data pack included in my contract. However, I have found that a great App I downloaded - NetCounter - is reporting cell traffic that is going to end up costing me a lot of money.

So I have a few questions.

1) How do I switch between running applications, so I can see what's running?

2) How do I prevent certain Apps from starting whenever I power on the phone?

3) How do I see what Apps are connecting to the internet(ignoring the WiFi) and creating unwanted cell traffic.

4) Is there something I can disable so that I can use the phone normally, but prevent it from connecting to the internet unless I am back home and using the WiFi connection.