OKCupid is making a lot of noise these days about requiring a phone number, right after Facebook themselves had a massive breach (267+ million numbers):
Either it's a bizdev scam that they're all trying to get in on, or they're clueless. I lean toward the latter but expect it to be the former. Surely they can raise ad rates with the extra PII, I'm guessing?
If I'm remembering right, they had two methods they'd switch between:
A. By emphasizing how much more secure it would make my account.
B. By telling me how many of my friends have provided theirs, which is a blatant attempt at manipulation via peer-pressure.