sorry if a search could've answered this for me, a bit strapped for time.
a users phone keeps getting these errors;
stack overflow
when you try to enter a zero:
input system error java lang nullpointer exception
when attempting to open the address book:
net_rim_bb_addressbook.app(263) not responding.
thanks in advance for any help...

What kind of BB device? Any 3rd party apps? You're probably going to have to wipe the device to figure out what's causing it.

corrupt handheld software perhaps?
I'd also say wipe it and if that doesn't do it, then reinstall the handheld software.
Maybe even upgrade it while you're at it?

thanks for the help. i just wiped it. something corrupt from our exchange server i suspect. thanks again for the assistance...