Nobody knows, but the last thing I expect at this convention is anything about a new iPhone (as hardware related).
Yes, we are fully focused on this iPhone/liquidmetal thing, but don't forget their new OS X Mountain Lion. Apple has already published that Mountain Lion will be released in "Summer" or "Late Summer", so I guess, next convention is related mostly to software releases (iOS6 and Mountain Lion) and maybe a new MacBook Pro line, because Apple will not release a new OS X without new hardware.
But of course, maybe they want start a huge firework with iOS6 and iPhone5 AND OS X 10.8 and MacBook Pro...THAT would surprise a lot of people...but I don't expect it.