Usually on android, there are two versions of apps that are available. One is free (with ads) and another is paid version (without ads). However, there is an entirely legal way to go around this restriction, without having to pay a single pence!
1. Root your android phone using unrevoked.
2. Download Droidwall
3. On the top of the screen, click on the "white list". Choose "black list".
4. Choose whatever apps that you'd love to block ads from. You know, stuffs like Angry Birds!! It was really annoying when all of a sudden, Vodafone ads came out of nowhere. hahaha, but no more problem now. :)
The only caveat is that, don't block any apps that use 3g/wifi because essentially that is how Droidwall works. It blocks the ads via denying the internet access to the apps. Kinda neat, don't you think?