My companies CEO had the same problem with his and since I'm the resident Blackberry guru I had to figure out why. Even with all the correct settings it still would only vibrate. I ended up reloading the software on the Blackberry (basically restoring it to factory defaults). This fixed the issue.
You will have to reload any third party programs on it and re-sync to get all of your messages and contacts on there.
well lucky for me i havent added many contacts yet i always do that last, incase something like this happens. So i download the new firmware (4.1), and try that? or is there a master reset type of thing on the phone that will do it?
This may be stupid a stupid response but I have the 7100g and found that I set the option in the profiles to "tone" but noticed that the volume for that option was set to "mute". I thought I was retarded when I couldn't get it to ring for me, which I may be, but at least changing that worked.
Some of the Blackberry 7100i models don't have their ringtones loaded correctly, so they won't go off when they're supposed to. A buddy I worked with called RIM about it, and they say that a hard reset (taking the battery out and putting it back in) should fix it. Give that a shot.