I have been having a problem with re-gaining a cell signal after leaving work - I get no reception in the building and usually the phone sits with zero bars or the little x all day.

BUT, when I leave the building, the phone refuses to find a signal. I cant make a call because the dialer stalls. Ive tried to toggle airplane mode on and off with no luck. The only thing that works is a full reboot, after which I get full bars because the signal outside of the building is fine. Ive reproduced the problem several times.

Anyone have any idea why this happens? or how I might fix it?
It is annoying to reboot every time I leave work.