PLEASE remember this point: taking a woman's telephone number is simple, very simple. The key is not to ask for it. You must tell her she's going to give it to you. Let me repeat this point again because it's crucially important: you do not ask her, you tell her.
Just use the following words exactly, or a similar version that works best for you:
You: "Jessica, I've got to go. But put your magic number in here (while passing her your phone) and I'll give you a call in a couple of days."
You: "Jessica, I've got to go. But put your magic number in here (while passing her your phone) and we'll do cocktails this week / tomorrow / whenever."
I have this thing for bar maids. I do not know what it is, but I just always seem to come across gorgeous ones. The problem is that they get chatted-up all the time, and so you really need to stand out. What's more, you've got to be quick, especially when the bar is busy on a night out.
You: "Hi there … If I order two drinks will you answer two questions?"
Her: "Erm … Okay. What can I get you?"
You: "I'll have two rum and Cokes with plenty of fresh lime please."
(She goes off to make the drinks and then returns)
Her: "That's 6 pounds / dollars please."
(I give her my card to buy a few extra seconds and keep her in front of me while I enter my PIN number in the hand-held terminal).
You: "Here's your first question … I get the impression you're single, am I right?"
Her: "Erm … kind of."
You: "Cool. Here's your second question … If I can find you a guy who's good looking, intelligent, funny, and who's prepared to put in time and effort with you – will you meet him for a couple of cheeky cocktails? "
Her: "Yeah of course!"
You: "Well put your magic number in here because we're going for a drink this week."
My experience tells me she will not say "No", but if she does you can always say: "What? You do not like cocktails?"
Tip: Do not knock it until you've tried it.
Tip: Some bar staff can not be seen to pass their telephone numbers out in front of supervisors, managers etc. So I've had women throw pieces of paper at me with their numbers on them in the past.