I recently upgraded to the Curve 8900 and also purchased a holster with the proximity sensor facility. When I upgraded, my profile was obviously automatically loaded onto the device because all my settings were there, including the automatic keyboard lock when placed in the holster. However, as a result of some work on the server, my profile was deleted and I had to reactivate the device. Now the automatic keyboard lock doesn't work any longer and I cannot find where to set it up again. The "old" route (Options/Security Options/General Settings) doesn't have this facility.
This is one of key aspects of the BlackBerry that convinced me to stay with it rather than try another type so I am very anxious to get it working again!