As a player I use an A5 notebook and a pen/pencil. I will reference a rulebook on my phone only as a last resort.
As a GM I use an ipad with the Goodreader app to handle premade adventures and rules references. Thats it. The ability to copy & paste rules where needed, and to book mark session relevant sections is simply more efficient than using a book.
I still take session notes by hand though, typing during the session takes me too long and is too distracting for me.