I think they will have to release a new phone, with some upgrades, or else they will fall way behind the competition... Apple likes to be on top, so I bet there will be an iPhone 5 or iPhone 4s Like you guys/gals said
In my opinion, I doubt there will be a 4gs or 4s or what ever. It will be iPhone 5. Don't you all remember the keynote where they said they were a revolution or what ever. The first released the iPhone. Then the year after they made the iPhone better by giving it 3G access. After that the iPhone got faster. Then the iPhone 4 was released and it improved with a new design, it got faster, two cameras and Facetime. If they made the iPhone 4 faster and called it iPhone 4s or 4GS wouldn't that be a step backwards? They would break the revolution!
While I do believe there will be an iPhone update in June 2011, I really doubt it will be called "iPhone 5". Apple will save "iPhone 5" for a major release of the next iPhone.
It will probably be called "iPhone 4.2, 4gs, 4p, 4f, 4pf, etc".
And as some suggested, I don't think they will skip numbers.
Example:
June 2011: 'iPhone 4pf"
June 2012: 'iPhone 5" (not iPhone 6!!)