If you’re an iPhone owner who’s still sitting on the fence when it comes to buying some sat-nav software, you might want to hold off a little longer.

Apple will release the next major version of its iOS software for the iPhone, iPad and iPod touch this autumn and turn-by-turn driving directions will be built-in.

This new feature comes courtesy of Apple’s own mapping app in iOS 6 that will replace the Google Maps app used in its iOS software since the iPhone first went on sale in 2007.

The new maps app has many new features (which include a photo-realistic 3D city flyover feature, similar to that Google recently announced), but the turn-by-turn directions with spoken guidance is by far the biggest.

Better still, the app also works with the Siri voice-recognition tool, which means it should be possible to say “take me to the nearest filling station” while driving and the iPhone will display the appropriate directions — which is much quicker and safer than swiping around the screen.

The only catch so far seems to be that like the Maps app currently used in iOS, the new app needs to download mapping data as required.

This might make it an expensive and/or impractical option on long journeys where mobile phone network coverage is patchy.

iOS 6 will be a free upgrade later this year for anyone who owns an iPhone 3GS or later model, but the turn-by-turn mapping feature will openly be available on the iPhone 4S and iPad 2 (or later models).

[More on Apple iOS 6]