Signal is dropping SMS support soon. It was one of the main features that I was able to convince my friends and family to use this app, a convenient all-in-one messaging app. Without it I'm not sure anymore, quite a baffling decision on their part.
I submitted a feature request and it was promptly denied. I got the impression they never really wanted to support SMS from the beginning. It was just a carrot even then, and they weren't going to focus any more effort on it.