Go to -
Sound Profiles>Edit Profiles
Select the profile you are using (i.e. Normal, Loud, Medium, etc.)
Select Phone (or Messages, etc.)
Select Vibration>Custom
Now you have the custom menu options displayed. Under - Vibrate, you have 3 options:
Always
Out of holster
In Holster
Mine vibrate but its very low vibration. It vibrate normal for me when out of holster.
Posted from my CrackBerry at wapforums.crackberry.com
Same with mine. At first I thought it wasn't vibrating in the holster at all, so I sent myself a test message and quickly holstered the phone. It vibrated, but it was so weak that I wouldn't feel it when the holster is attached to my belt. It's all good though...at least I can HEAR this one make a noise in the holster, unlike the Tour that this phone replaced.
I have the same issue, and I see that others have the same S2 complaint. When holstered, I can clearly *hear* the phone vibrate, but can barely feel it. I'm not certain whether this is related to the stock Verizon case, although my old Storm 1 had no issues in the same stock case. I wonder if others have had better luck with a different case.