I am in a very similar situation to you abelcd. I'm starting a quantified self/social app and am currently considering onboarding/authentication, so I'm very interested in contributions to this.
I can see the benefit of having mobile signup as a means of minimizing friction to maximize conversion. Email signups are a big pain-point and many users just don't trust OAuth means. My own target market has a strong preference for signing up through email vs. OAuth (I didn't test the market on phone signups), but email signups presumably have bad conversion rates vis-a-vis phone number signup.
I can't find comparable figures, but the Digits signup team claim an average conversion rate of 85%, which sounds impressive at least. That said I can forsee numerous downsides (less access to uesrs' social media contacts, less ideal login on web, user management etc). But with email decreasing in importance for young people - and if OAuth remains unpopular - I wonder if phone number signups is the future of app onboarding. Any thoughts?