I'm guessing Oct. but they REALLY should release every 6 months starting after the 6.
Why would anyone want, need, or expect Apple to release a new phone every 6 months? Hell, it took them almost 3 months just to catch up to the demand for the 5s. How much could they even improve each model? People already complain that the "s" models are only slight upgrades to their predecessors. This suggestion is not practical or necessary.