please anyone tell me about the quality of the speakerphone of 7650. is it clear and loud? how the sensor works: is it too sensitive? how stable the speakerphone mode?

The speakerphone is OK, but thr RINGING is not. When the phone is ringing, the sound is not loud enough.

I think this has something to do with the OS, because when I play games the sound is LOUD (TriplePop), but the ringing sound is less.

I don't think the speakerphone on the 7650 is a patch on the 9210's. So, while it is good on the 7650, 9210 owners will be somewhat disappointed.

so, how can we supposed to reduce the volume while playing games..?

TO reduce the vol. when playing games, go to Profile->General and reduce the volume there.