I have a BB Curve 8520 and was supplied by the Vodafone shop with a nice leather case/holster with the magnet at the top.
When I put the phone in the holster it sleeps half way in then comes back on when past the half way point! However you try the phone will not stay asleep fully in the case!
Could this be the wrong case and should the magnet be at the bottom?
I think most of the 8900 stuff is compatible.
The side entry swivel holster i have (originally ordered for 8900) is now listed as 8900/8520, works beautifully with auto-lock
I have my new holster and it sleeps the BB perfectly every time. I have now been able to allocate my left button to the message folder instead of keypad lock. Only problem is Holster has belt clip which I could have done without as I prefer pocketing it!