Model Release date Notes
1 June, 2007 Origin
3G July, 2008 New in 12 months
3GS June, 2009 Upgrade in 11 months
4 June, 2010 New in 23 months
4S October, 2011 Upgrade in 16 months
5 September, 2012 New in 27 months
Pardoning my inability to format this chart on an iPhone, the release cycle for Apple hardware is getting longer over time. Apple could upset this trend, but based on the data we shouldn't see the iPhone 6 until 2015, and we should get a 5S by early 2014. Not worth waiting for new hardware if you want a phone now and you want an iPhone.