The expected iPhone 5 would actually be the sixth iPhone model.
Although Apple hasn't announced a name for its next iPhone — or even confirmed that one is coming — a "5'' in the shadow of an event invite suggests that it will be the iPhone 5.
Here are Apple's iPhone releases since its debut in 2007:
— iPhone, June 29, 2007, starting in the U.S. (announced Jan. 9)
— iPhone 3G, July 11, 2008, starting in the U.S., Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Hong Kong, Ireland, Italy, Japan, Mexico, Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, and the U.K. (announced June 9)
— iPhone 3GS, June 19, 2009, starting in the U.S. (announced June 8)
— iPhone 4, June 24, 2010, starting in the U.S., France, Germany and Japan and the U.K. (announced June 7).
— iPhone 4S, Oct. 14, 2011, starting in the U.S., Australia, Canada, France, Germany, Japan and the UK (announced Oct. 4).
— iPhone 5, to be announced