Blatant excuse to post the following video:-
But seriously, folks...
Nick, who cooks my Full English breakfasts in Henley-on-Thames, gave me his wife's BlackBerry Bold 9700 to look at, as it had an odd fault. With the headset plugged in, it worked fine. With the headset unplugged, the phone oscillated between using the internal loudspeaker and the headset socket about once a second, rendering the phone unusable.
After many hours of unsuccessful tinkering, I decided to take a look on Google to see if anybody else had successfully cracked the problem. I saw THIS. It appears to be a common problem with BlackBerrys, with lots of spam sites offering unlock codes to "fix" it.
Having upgraded the phone software from V5 to V6, the fault was still present. Therefore, it's not a software problem. Therefore, unlock codes won't fix it!
It's a hardware problem. It may be a design or a production problem, but the pull-up on the headset socket is too weak/has failed, resulting in the voltage on the headset present/not present control line falling towards "present" when the headset is not present. This may also be caused by moisture in the headset socket.
As the above control line interrupts the processor (as an instant response is required on plugging/unplugging the headset), there is major disruption to the phone's operation.
A fault like this is easily fixable by a reputable mobile phone repair shop. A resistor value change or solder joint rework is all that's required.
EDIT: As of 11th April 2012, Blogger is no longer compatible with the default BlackBerry browser. Basically, my BlackBerry is not working!
I am now using the Opera Mini browser. If I display emails on the BlackBerry in plain text, I can open links using Opera Mini, which works O.K. with Blogger.