Apple has released a new iPhone every year since it entered the smartphone market. Here are first launch dates for each model:
Original iPhone: Friday June 29, 2007
iPhone 3G: Friday July 11, 2008
iPhone 3GS: Friday June 19, 2009
iPhone 4: Thursday June 24, 2010
iPhone 4S: Friday October 14, 2011
iPhone 5: Friday September 21, 2012
Reports indicate Apple plans to reveal the iPhone 5S on Tuesday, September 10th. The device is expected to be available on Friday, September 20, 2013.