I upgraded from the 9800. I had the otterbox case and had ordered the 9000 case from Amazon after reading about it on this forum. When I purchased the 9900 i purchased a case in the ATT store. It was way too tight of a fit and did not put the phone to sleep as advertised. I pulled out the 9000 case and it fits great. Not too tight a fit and the magnet puts the phone to sleep. A great solution and e en better that the cases can be purchased for around $5.00.
I have a side case that used to work with my curve, but it won't make the 9900 go to sleep, I guess the magnet is in the wrong place. The free case that came with the Costco Bold is so incredibly crappy, I'm afraid it would scratch the phone....it didn't, and I only tried it to see if it would make it sleep, which it didn't! I got a magnet from the car and found that my phone is capable of sleeping, so I guess I just need the right case.
The Otterbox Commuter, looks like it doesn't put the phone to sleep?