I have had it a lot of times and have sent three blackberries back to RIM because it appeared no-one in our supplier and no-one at RIM actually knows how to stop this particularly irritating problem. It once happened 4 x in one day and now happens approx every fortnight, normally just when I need to use it.
The old hard re-boot of extracting the battery and sometimes cleaning the SIM is as atrocious a "fix" as Bill Gates' original response to Blue Screen of Death which was to reboot your PC!!!
Let's face it, if all the lights in your house kept going out and all the electrician could say was "Well, go to your fuse-box and reset them all!", you would fire him and find someone competent.
It is well past time RIM fixed this really annoying "feature".
