Can one add email contacts to the Kitkat Email app? (as in iOS7)
Android tends to work better with Google's mail (Gmail). I don't have any knowledge specifically of BT as I am a Yank, so I can't address that. I just read up on the BT/Yahoo split and looked around for a couple of minutes for a solution for you, but it didn't look good.

I would recommend Gmail and then grit your teeth and make the switch.