Mathematics isn't particularly unique on this front.
While professional writers are often typing out their work and yet occasionally when you are driven to jot down an inspired idea you just reach for the closest writing instrument. Computer, Napkin, Journal, your hand, whatever.
My experience has been that professional mathematicians are very much the same way. All communication between professionals is basically typed. The symbols required are not really much of an issue given our typesetting languages. We use latex here (And so do all mathematicians really) and I can produce the oddest of symbols pretty darn quickly.
Integrals and greek letters are pretty tame in comparison to what the technology is capable of...
Anyway just like the writing industry the fact that we CAN communicate very efficiently via computers doesn't really stop most mathematicians from asking the waiter for a pen so we can jot a thought down on the back of a napkin before the thought is lost into the ether...
Paper writing isn't going away for either discipline. But correspondence is now almost exclusive digital for both disciplines.