My friend married a profound deaf man, she reared her children and learned to sign with only one hand, multi tasking, over the years he's had a stroke, resulting in one side of him paralysed, he signs now with just the one hand. nothing to do with the mobile phone really, only, you can sign with one hand
You can, of course, Ean.......but to sign and pass exams in BSL as I had to you need two hands,.......but to sign whilst drinking a pint of G...one hand will do...I'm quite good at that..... ;-)
I bet you are ;} her children grew up on the one hand learning and her grandchildren do it that way too. I was often sat in her kitchen chatting and beside me the other hand was going 10 to the dozen at him, I'd just stare at her and say, "have I come at a bad time"? she'd shout no! the shout was meant for him in sign - we'd have a good laugh about it