Phone Etiquette

We were driving in the car today and this is what I heard in the backseat:

(Keegan is jabbering on his play cell phone to Grandma.)

Connor: Hey, Keegan, did you see that?

Keegan: I on the phone.

Connor: Keegan, did you want this? Keegan? Here, take it, Keegan.

Keegan: (Still jabbering into phone.) I on the phone. That rude. Connor, I on the phone. That rude, Connor.

Hmm...what do you think I tell the boys about interrupting me when I am on the phone?