It works for me in dating. Most guys when they talk to a girl will ask for her number so much so that most women are auto-programmed to play hard to get about giving out their number.

So I tried something and it works a lot better: I ask them for a concrete date/time we can meet again for a date. I give zero importance to their number. Qualitatively, I think most girls are "shocked" and not used to someone telling them their phone number is completely irrelevant.