For instance, maybe verifying a new number over SMS should cost $0.10 if that's going to make up 14% of the operating costs.
Begging for donations to subsidize excessive use by other users just doesn't seem sustainable.
Hard disagree. If you charge, the number of people who will use it shrinks by several magnitudes, and then you lose your network effect, you lose the ability to get your less technically inclined friends to install it.