@ peglo, welcome to the android world. fret not for help is at hand. here's how;
1. Go to android market and download an application known as Smoda widget.
2. after the download is complete long press on the homescreen, select add widget, choose smoda from the list of Widgets available. you should now see a smoda widget on the home screen. appears as a small square with a green tick or red cross depending on the status of your 3g connection.
3. what smoda does is that it acts as a switch that can turn your 3G connection on and off thereby saving you tonnes of airtime. you can switch it on when you want to access net and turn it off as soon as you are done surfing. this will also make your battery go for a longer period without needing a recharge. try it and post your feedback here.
4. as some1 suggested, always go for data bundles. for phone surfing, I always prefer the daily internet bundles on offer from safaricom (*544#). if you choose this option, I'd recommend you also download the app, 3Gwatchdog, which shows you how much data has been utilized and can warn you as you approach the daily quota.
happy surfing!
It is a curious fact that of all the illusions that beset mankind, none is quite as curious as that tendency to suppose that we are mentally and morally superior to those who differ from us in opinion.