“When you use Signal, your data is stored in encrypted form on your devices. The only information that is stored on the Signal servers for each account is the phone number you registered with, the date and time you joined the service, and the date you last logged on.”
They used to have that functionality (and I loved it) but they removed it due to it “not being secure enough” for their standards
Signal can absolutely replace WhatsApp, Viber (although I never heard of it before), etc. It supports voice and video calls, and you can even screen share from desktop
I was so bummed when they removed that feature. I didn’t really understand why viewing SMS in the app was “not secure enough”.
I guess they have some criteria for security and they don’t want to “ship” features that are below that (SMS is the most insecure you can get).