That's been part of my anti-censorship arguments for a very long time. There's no technological reason why your phone calls can't be monitored and controlled just like any other medium, such as Facebook, Youtube or Twitter.
Unlike tech companies( Facebook, YouTube or Twitter) phone companies are common carriers. There are a lot of legal reasons in the US.
Also, phone calls are 1:1. Most deplatforming is in the 1:many space
There is a treasure trove of data awaiting us on Zoom, Discord and Skype to name a few.