My 2 cents.
/800\-555\-^9{4}/
Update
The above didn't fully meet the requirements thanks
zer for pointing that out.
I would suggest using
Roy_Johnson's approach as others have suggested.
-InjunJoel
"I do not feel obliged to believe that the same God who endowed us with sense, reason and intellect has intended us to forego their use." -Galileo