I know there is an application that can disconnect 3G / HSDPA data connection after certain period of inactive usage. But I failed to make it to work. So I disconnect 3G connection manually all the time with lot of clicks of course. Yeah… Again, part of Sense 2.5 tweaks & mods bring us ~ Touch X Data Disconnect. It will disconnect your data connection with just 1 single click. Disable 3G connection will help you to save mobile phone battery. A must install quicklink for my HTC HD2.