In windows phone 7, there hidden menu meant for debugging purpose named as diagnosis, some call it MFG menu, some call it EM (in Dell) , to goto your Diagnosis , all you need to do is open your dialer and type :
##634#
And thats it, in a moment, it will show you a new dialer, actually, now you can provide any code you want to change respective settings, below are few, you can share yours, I will add them here.
*#7284# : Lets you select how USB behaves, default is ZUNE Sync, you can change it to modem, whatever option you see there.
*#0*# : General hardware test, you will enjoy it, it lest you test your front camera, accelerometer, LCD test etc etc.
*#22558463#: Total call time for you phone.
*#2*# : Battery diagnosis and information (lots of )
I will try to add more if I find them.
Advert.