Prior to iOS 6, opening a URL from an iOS device pointing to maps.google.com would launch the native Google maps application. However, since Apple has replaced the Google maps app with their own, you need to change the URL to maps.apple.com to open the new native maps app. If you are still using iOS 5, maps.apple.com will redirect to maps.google.com and use the Google maps app.
More information can be found here:
http://developer.apple.com/library/ios/ ... Links.html