Unfortunately, removal of the SMS function was what caused the few friends that had Signal to stop using it, myself included. It was great to see someone show up as a Signal contact instead of regular SMS, but also being able to reach anyone I needed without having to figure out whether they have Signal, so I can use that, or that they don’t and I have to send an SMS. Now I simply don’t bother with Signal and just use regular SMS all the time, and I don’t think I’ve opened Signal ever since they removed SMS support.
Which is a shame, I really liked Signal.
Dropping SMS alas was necessary (and not just for Signal, but for messengers-with-SMS as well) because of the general play Google is doing with SMS → RCS. IMO, Signal held the idiot ball quite strongly by not just picking TextSecure from their old archives, tuning it up and releasing it as an updated, separate “Signal SMS” app.
I feel like they could’ve just put text messages in one tab and Signal messages in another tab. Like, iirc, their whole deal was that they were opposed to potentially misleading people about text messages being secure just because they were being sent through Signal.