The telephone ring tone on my bb seems to change of it's own accord from time to time. The other day I almost missed a call because I was in a public place and I didn't realize it was my phone ringing because it was a different tone than I had set.

Has anyone else encountered this . . . . ?

The only other explanation I can think of is one of the people I work with is resetting my ring-tones as a gag. . . . . . my bb is rarely locked . . . .. however, it virtually always in my pocket or in my sight.

Or maybe I am just hearing a ringing in my ears!

Wirelessly posted (8700g: BlackBerry8800/4.2.1 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)

Maybe you are-or maybe the coworker is pulling a fast one on you.
Unless you have an exception set for certain callers, the BlackBerry ringtone won't change on it on.
You can set the profile to LOUD when you desire.