[chris_va]

I chose to do Facebook and email/password.

SMS costs a very tiny amount of money, and didn't offer any advantages (you can't get at the user's phone # on ios, so you cannot prefill, thus email had a similar level of friction from the user's perspective).

[pyvek]

I've seen some of the large websites in India offer OTP (one time password) login using SMS, which I personally have used many times. You enter your mobile no, get an OTP and login with that. Removes the hassle of remembering the password.