Gday after much more research.
apple have advised the same as you we only have the one model sold in australia. (the GSM model)
But with enquiries to the store and technicians they have answered much more clearly. They have informed me it doesnt have anything to do with the phone materials when it comes to coverage on iphone. Both 5c and 5s are made the same specs only with the obvious extra processor and upgrade. For coverage it would come down to the provider through software installation. From the description they gave is, the phone provider has set the bands for the phone to give the extra coverage. To their advice the provider has not allowed this phone to have regional coverage. But this can be changed later down the track if the provider wish to do so and would be done automatically.
Suprisingly i did speak to someone also from telstra who knew a bit about it, and the response was the same as to it can be automatically set later down the track.
So as far as the 5c being plastic/different materials is better for coverage reasons, a technician from apple has confirmed that it makes no difference. if not the 5s should be slightly more powerful but in no way does the metal backing interfere with antenna. both phones had similar results.
i hope im not stepping on any toes but i made quite a few calls about it as quite a few mates i know also want to find out, and also getting mixed answers.
other than that cheers and i its good to see a site like this.
