I sent my a900 for routine sensor cleaning and calibration, thru IMM Sony Center, about 2 months ago. Quite surprised they only charged me "handling fee" of less than $10 (can't remember the actual amount).
This was the 1st service after my warranty has expired, which was back in late 2009, so dunno why they did it for "free". I even requested the counter staff to patch me to the technician, just to check they really did the job, and he (the technician) assured me he did. In addition, my settings are all jumbled up upon return, so apparently, they did do a thorough check and calibration. The inner part of the body did look cleaner too...