See Android 4.2.1 Jelly Bean running on the T-Mobile G2 thanks to CyanogenMod 10.1
Unfortunately, the T-Mobile G2 was never updated to anything beyond Android 2.3 Gingerbread. That, however, does not mean it can't run anything newer, albeit in the form of a custom ROM provided by the CyanogenMod team. What you will see in the video below is Android 4.2.1 – the platform's very latest version released to date, installed on a T-Mobile G2. And as a matter of fact, the smartphone performs much better than you might expect, even though the hardware inside it is a far cry from what powers today's high-end smartphones.
XDA Developers forum for further information before proceeding.Now check out the video below and if you have a T-Mobile G2 lying around, perhaps you might give this custom ROM a try. Just make sure you head over to the