With Apple actively working on the sixth-generation iPhone which is likely to see a public release towards the end of this year, users of older generation devices like the iPhone 3GS and even the original iPhone could be forgiven for thinking that the time has come to look for an upgrade or purchasing a more up-to-date unit. The core functionality of the iPhone has remained stable since 2007 but the hardware has greatly improved with each release, with the most notable changes coming in the form of the Retina display with the iPhone 4 and incremental processor and memory upgrades.