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Apple Maps uses Siri for turn-by-turn directions. For Apple to make it possible for the iPhone 4 to have turn-by-turn in Maps, it would have to develop a special version solely for that one device that didn't use Siri, which would cost a lot of money. Apple does much more than most companies to keep OSes up to date for years after the device was first sold. Think about it - the iPhone 4 is nearly 3.5 years old now and Apple is still updating iOS to support it. That's pretty great.

And, just to stay relevant, I've been using Maps exclusively on my 5c since I got it two weeks ago and it's been as reliable as Google Maps had been. Apple seems to have made great strides since the appalling release of Maps last year.
 
Apple Maps uses Siri for turn-by-turn directions. For Apple to make it possible for the iPhone 4 to have turn-by-turn in Maps, it would have to develop a special version solely for that one device that didn't use Siri, which would cost a lot of money.

I often hear that directions use Siri, but that does not make any sense to me. Directions don't use Siri. You can start the directions right from the maps app without any voice activation.
Are you referring to the voice that is used? That isn't Siri, and the voice is already available on the iPhone 4. The "Speak Selection" option is available to speak any text that is selected, and uses the same voice that Siri uses.
 
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