Firstly, not everyone has a mobile phone. What ever moron made it mandatory should be sacked. You are discriminating against those who don't want a mobile phone or are made ill by the radiation they emit. It is illegal to this in Australia.

Secondly, you do NOT need someone's exact date of birth. Asking for the year of birth is sufficient. The number of times Yahoo is hacked it is an extreme security risk and the only reason you would ask for it is to sell it.

This will cost your company as I will be recommending my clients stay away from all Yahoo sites for their own digital safety.