There is the David DeAngelo method (whether or not he actually came up with this I have no idea, but this is where I read it from). Anyway, he originally had this for a way to get a girls email in under 3 minutes of meeting her but with a little tweaking it could be manipulated to fit a number close.
So say you have her entranced in conversation, whether you have just preformed a cold reading or whatever she should be very interested in you. Then the conversation should go like this:
HB: Wow that was amazing! (presumed you have just preformed a magic trick or something).
PUA: Yea but I have to get going, I've got stuff to do.
HB: No! Can't you just stay for a little bit?
PUA: Look I've really got to get back to my friends, but clearly your interested in me..but I'm still not that sure about you though. I usually make girls work a bit harder for my number...*pause and pretend to think*...so I think ill do the same with you *big smile from you*.
Pretend to walk away. Then turn around and say,
PUA: Well, I do think your pretty cute/sexy/ok, so right your number here and I'll give you a call.
If she doesn't like this idea or seems drawn back just say that you really have to go, but if she has email write the address there. Email is a lot less invasive and i think you can be quite playful via email. If shes an 8 or above, maybe do a ring/necklace routine and walk away.
My favorite, cocky/comedy, push/pull, and number/email in one routine. VERY effective
- Memento