Radio was a bad analogy but how about books or newspapers? As another commenter has mentioned in this sub-thread, there has always been some kind of attention divide like screen has been for our age. Also, we may discard books as a source of distraction but my question is whether it is so because we are used to it.
Books/newspaper are indeed something else, but still quite different. I'm not sure if this is too general, but I don't think anybody takes a book everywhere he/she goes, and picks it up in the middle of a conversation to read 1 or 2 lines, then put it back again.
For example, try at same time reading (and properly understanding) a mail and have a conversation with somebody. Then try having a conversation with somebody while music is playing, no matter how loud. Ok it gets harder if you actively try to follow spoken words on the radio, but you get my point.