Which devices support iOS 7's burst mode?
According to TechCrunch:


  All phones capable of installing iOS 7 get a variant of burst mode, in fact, which takes pictures in rapid succession, but not at the 10fps rate of the iPhone 5s, and without the auto selection feature that suggests which shot is best.


And CNET:


  What Apple didn't mention is that older iOS devices would also be gaining the ability to take photos in succession, just not nearly as fast or with the same software powering the editing process.


TUAW:


  You can use burst mode on older models of the iPhone, and it works pretty well, but you don't get the speed nor the auto-selection mode that burst mode on the iPhone 5s has.