Audio navigation using kml / kmz / gpx file on iphone?

Hi All,

I'm new to riding and today decided to have a first ride from work back home. Because I don't want to go through busy roads - I used http://www.bbbike.org/Perth/ to find me a route through side streets. Great route but no way I can remember all turns without navigation.
I exported this route to gpx / kmz / kml format, I can display it on different maps / GPS trackers etc - but can't find a way for audio navigation.
I will be riding against the sun - so reading map form the phone would be a nightmare. I thought that there is app which guides you using audio (like google maps) for customized gpx tracks, but I cant find anything.

Anyone have any idea how can I have customized track audio navigation in my iphone? even if i have to purchase app - I am ok, as soon as it works.

Thanks,
Karol