That question is a little incomplete... what's the situations where you are asking the number? what kind of vibe?
If I'm at the bar, and talking to a girl and there's a good vibe I'll ususally say 'give me your number so if I lose you later that we can still talk'.
I ususally save a kiss to find out if it's a waste of time quick. A girl will give her number before kissing, but if she gives your number and then kisses you back well that's good.
Last is the kiss test : Where you kiss the girl open mouth, but pull back just a bit too soon. The test is 3 way.
- She pulls away from the kiss = chuck the number she's not all that interested
- she kisses back = you're in, but on a short rope... don't fvck up
- She kisses back and moves in when you pull away = Done! I usually think to myself "you might as well get naked and bend over now, cause you'll just do it later."