advice to my future niece or nephew
My brother and his wife are expecting a baby early next month, and I have a bit of advice I want to pass on to my prospective niece or nephew:

When it comes to meeting someone you consider a romantic and/or sexual prospect, giving that other person your number (or email, or whatever we will be using in the year 2018 when my niece and/or nephew gets interested in such thing) is all well and good, but it is basically irrelevant. Get the other person's number. Without that, you've got nothing, and you're at the other person's mercy. With it, you have some degree of agency. Even if you call it and get a laundromat somewhere, you've got a hard fact to work with.

People may take other people's numbers and make vague noises about calling, but it is in no way an obligation or anything you can depend on. They make take your number with no intention whatsoever of calling back, out of a desire not to make a scene, or even some misguided benevolence to let you save face, but it's still an empty gesture.

I formulated this idea after giving out my number to someone I met Saturday night, and realized that I had no way of reaching her. Now, said person did, in fact, call me tonight, and I did appreciate that very much. There is even tentative talk of coffee next week. However, I made sure I got her number. Why? Insurance.