That is not true. I have a Facebook and no where have I ever been required to give my mobile number. I think you only need an email (and I think, it doesn't even necessarily have to be valid) to create an account.
> "...spend a questionable amount of time"
I created a test account for an app I'm working on (the other month) in less than 5 minutes, give or take. For an app you are building with their API, 5 minutes of time and getting to use it for free is the same as "($50/year)" as you mentioned? That seems a bit exaggerated to me.