mbay2002 offers the only work-around available right now that I'm aware of but, unfortunately, it's only half of a solution. I have different in-holster profiles set up because sometimes I want an audible tone for calls/messages and sometimes I don't when my BB's on my hip. Thus, if I'm using my most-used profile, I'd still have to switch profiles to get to a silent-in-holster version before putting it in my holster at beddy-by time...
It's been awhile and I'm no longer certain, but I used a Sony Ericsson T610 for about a year and, while a BB blows it away, one great OS feature I think it offered was full user customization, including the ability to switch profiles at designated times. Regardless, this isn't hard to program, and I hope that as BBs continue to move more into the consumer mainstream, this will be a feature RIM adds. I've e-mailed RIM this suggestion, and I encourage you to also...