sounds like askin numbers on the street
it's not that difficult actually by askin straight away.. but the
success rate? It's random. Whatever it is, just dont pin too much
high hopes tho, then the rate of disappointment will be lower. If
she rejects, well, not too big a deal, dont show a black face
immediately, be a gentleman, tell her it's ok, chat a lil and go.
Switch target then, dont be disheartened 
Fake numbers? After you get her number, call her at the spot. Give
her a missed call that is. Let her have your number too 
i'd prefer to be straight-forward and make my point clear that im
sincere in makin friends with her and in hope to get her number,
and not usin her phone and call my phone instead
sincere, direct, st8-4ward