phone numbers

There is something to say about the scary moment when someone asks for your phone number. The scenario can go a few different ways but it seems to lean one way for me, kind of like the way I lean more blue than red or left than right.

Scenario #1 (most common for me)
Boy and girl flirt for a length of time, exchange similar stories and enjoy a few laughs. A kiss might be shared - or not - and the end of the party nears.
Boy: "So I should get your phone number before you leave."
Girl: "Hm, maybe/ok"

TIME-OUT: I do not like the way that the boy asks for the phone number. It shows no real interest. Why do you want the phone number? For an actual reason or just another girl's number to have in case you need someone to hang out with?
Plus, I don't really like the fact that there is no answer for the girl. It wasn't a question, the boy made a statement. Awkward. Why?

Girl (inside of her head): I don't really want to give him my phone number. But now how do I make the phone number thing go away? Will he forget? I can't make one up because he'll call right there so that I have his number. This is the dumbest of all new trends for boys and girls. Don't call me so that I have your number. So laaaame!

Back to the scenario...
Boy: Hey, you've got your phone out, you should take my number.
Girl: Ummm....(I need THINK TIME PEOPLE!) OK.
Girl (thinking): I am not going to call you. I don't want to because I am not interested. This is not flirting, this is making a business network contact.
Boy: *punches his number into girl's phone* *clicks 'send' on my phone so he has my number.
Boy: You should call me sometime. Seriously. We should hang out.
Girl (inside of her head): I am not interested. I will ignore your phone calls. I am not interested.

Scenario #2
Boy and girl flirt. Boy gets the girl's phone number through a friend or by asking her to meet up outside the current venue and then needing her phone number because they will be meeting again. There is a purpose in that!
Girl (inside of her head): I can't wait to see him again....

Question: How can I be polite and say no to giving out a phone number?