I know this was requested many times, so today I gave another shot at AdMob plugin for Android and although it took me whole day, maybe this time it was successful.
Well at least you all ought to test it
Wanted to say thank you to @hgvyas123
for initial version, which unfortunately did not work on my android, but I took a lot from that plugin code and it really eased the understanding of how plugin works. Basically this plugin uses weak reference to activity, which I think also solves the problem for older Androids, so at least now it is working on mine Android 2.2 and Android 2.3 phones.
And introduced couple of additions as providing ad type, etc.
So here's the plugin itself, Android project with plugin code and Gideros example project, as well as installation and docs for usage:http://appcodingeasy.com/Gideros-Mobile/AdMob-plugin-for-Android
If you find anything wrong or not working, post here and will try to resolve it