Sync music playing on 2 iphones

Is it possible to wirelessly sync music playing on 2 iPhones that are in close physical proximity to each other?

The first phone is primary, playing a local collection of tunes loaded onto it with iTunes. The second is "slaved" off the first, simultaneously playing whatever the first is playing.  Like an old-style pair of speakers connected to a single amp.  Can't rely on internet connection to make this happen. 

More generally, I'm looking for a way for 2 people wearing conventional earbuds to listen to the same music at the same time.

The concept is simple but I'm thinking it can't be done.  Any thoughts?