The iPhone 3GS and iPhone 4 won't get turn-by-turn directions and the flyover feature found in Maps, Apple's alternative to Google Maps. They will also not be getting the Siri, which will be coming, however, to the new iPad. However, Apple is still bringing iOS 6 to iPhone 3GS and iPhone 4 and continues to market the 3GS as a budget device.

At its WWDC conference on Monday, June 11, Apple said 80 percent of its users were running iOS 5 - compared to around seven percent running Android 4.0 (Ice Cream Sandwich). However, Apple isn't bringing complete compatibility to all of its supported devices: the iPhone 3GS and iPhone 4, despite the latter releasing in 2011, will not support turn-by-turn navigation and flyover mode in Apple's new Maps app.

Flyover mode is a 3D view of cities, while turn-by-turn navigation in maps was described as the best-looking implementation of any GPS service by tech site The Verge. Apple devices running the A5X chips will fully support the OS: the iPhone 4S, iPad 2 and the new iPad. The tech giant hasn't specifically explained why only its latest devices support the features, but the most likely reason would seem that the older hardware is incompatible. It's also been confirmed the iPhone 4 won't be able to use Facetime, Apple's video calling service, over cellular connections (3G).

In Apple's demo, flyover was noticeably stuttering (presumably on the iPhone 4S). Rendering a city fully in 3D probably isn't possible on three year old hardware, in the case of the 3GS. Undoubtedly, jailbroken iPhone 4s will access flyover to see if Apple's limitations are justified. When iOS 4 introduced multitasking, jailbroken iPhone 3Gs could use multitasking. The results weren't good.

The iPhone 3GS is also missing shared Photo Streams, the ability to set VIPs and flag e-mails, along with offline reading. iOS 6 users can set VIPs to receive a special notification when a message is received. While it may seem strange to suggest a device can't support offline reading, or minor e-mail functionality, it may be the overall impact of running a fully enabled iOS 6 and the impact that'll have on the user experience. The 3GS was released three years ago, with A4 chips.

Apple's WWDC conference can be tracked online.