[Blackjack]

I find that if I'm likely to meet the person again, I won't even bother with the phone number - I'll only ask for it when I need it i.e. have a genuine reason to call her that isn't small-talk related.

Failing that, if you get to know her and reckon she likes you, ask for her number from a friend or whatever and send a nice innocent little "Guess who!!" text message. Works every time!