Re: @Phil W - multiple PINs?
It generally isn't three extra numbers, because unless you're in a huge city there are only a dozen prefixes or so, then four digits.
Anyway, people USED to be able to remember those numbers, but no one I know remembers numbers these days ("in case they have to use a pay phone"? Are you posting from 2005? They don't have any around here anymore)
In fact, when I exchange numbers with people, sometimes they don't even know their OWN number, and I give them mine and they text me so I'll have theirs.
I'm sure a few more numerically inclined (i.e. more geeky) people will think having a dozen PINs to open every app they commonly use automatically is a great thing, but creating features that 1% of people might use is a waste of time.