This is from the TOS link posted earlier in this thread:
Additionally, with your permission, we may contact you via phone or email to provide you with promotional offers regarding Microsoft Online Services. You may change your contact preferences in the account management portal.
>>>BTW, I have been asked for my phone number when purchasing something in a store on more than one occasion, so that little analogy you made earlier is more real than you seem to realize
Indeed. Would you continue to shop at that store if they required your phone number? Interesting story: There is a grocery store chain here in So. CA (Albertsons) that was doing very well until a few years ago when they switched to a pricing model that required customers to swipe a store ID card in order to receive discounts. I immediately stopped buying there. They recently closed about half their stores. Now, I am not 100% certain the ID cards where the only contributor to their downfall, or even a primary contributor. But their stores got really empty really fast right after they started doing that.