You've heard of photobombing of course.  Well, this is kinda-sorta like that, except with cellphones.  Nevermind - just watch the video- it's hilarious.  

I guess the guy in the video produces these little pranks for YouTube with his wife, who is the videographer.   They basically sit next to a person who is having a conversation and they....let me see if I can explain this...they take the part of the person who's on the other end of the line... never mind--just watch this.

Very funny.  Would you have the guts to sit next to someone and do this?  I would say not to try this with just anyone.  You might get "round housed" by somebody.   Kudos to these folks at "Mediocre Films".