KMZ and iphone

For me the easiest way is through the app MotionX GPS.

Buy MotionX (A few dollars)

Follow the manual to download the maps you need so they are available offline

Go to http://www.gpsvisualizer.com/convert_input and convert the file to a .gpx file

Email the file to motion x
They will send you a return email, open in motionx, and you have the track on a base map---always, even with no cell data or wi-fi with a little blue triangle of your position.

There are many other ways, but the best software is the software you know. MotionX is worth learning.

The format you need for the GPS tracks depends on the software you will use on your iPhone. KML will definitely work on your phone -- you can get Google Earth on your phone, for example, and then load a KML file into it. The drawback of Google Earth, of course, is that you need an active Internet connection. Not always desirable if you'll be incurring roaming charges!

If you are looking to use the GPS tracks offline, then you need a different GPS app for your phone. You need to find out what formats are supported by that app. Lots support KML as-is. However, almost all GPS apps support GPX. Thus, if you convert the KML to GPX format you should be able to use the GPS track in almost any app (or on a traditional GPS device, for that matter).

There are lots of free options if all you are trying to do is convert from KML to GPX.

GPSBabel is an excellent option. It's free and works on almost any major OS (including Mac). You can get it here:

http://www.gpsbabel.org/

It supports a massive number of formats and the conversions are very reliable in my experience.

For working with your KML / GPX files, Route Converter is highly recommended. It is free and also available for both Mac and Windows. You can get it at:

www.routeconverter.com

Route Converter is handy because it makes it very easy to tweak the GPS tracks.

I use both of these regularly (almost daily), in addition to Google Earth and various other tools. Well worth looking at.

Have a great Camino!