You can't overclock an Android phone without superuser (i.e. Root) access. The G2 can't easily be permanently rooted, but it can be rooted until you next reboot I believe. The app z4root (free on the Market) can root 99% of Android phones (if you use the temporary root method it offers). You can then use setcpu or similar to overclock your phone. Be careful of course, CPUs were set at a lower speed for a reason (heat and power limitations of the phone).
