JustCamera is iOs app. It allows use iPhone or iPad as web-camera with JustBroadcaster. Audio supported!
Of course you can buy Logitech web-camera ($80+) but it's not necessary if you have iPhone.
So what you need:
1) Lighting cable for connect iPhone to Mac
2) Mac (iMac, mac mini, MacBook) with JustBroadcaster app (any version - for Facebook or YouTube)
3) iPhone with JustCamera