Having been available to Android and Windows Mobile devices for some time, Google Latitude
can be now used by owners of Apple-made handsets. The extra feature will allow you to see the current location of your friends and buddies and Google has revealed that they and Apple have worked together to deliver a version of Latitude for the iPhone, that is most comfortable and handy to use. That´s why the function is available via the phone browser and not through Google Maps. According to Apple representatives, so as people don´t get confused.
To make use of Google Latitude, you need to have an iPhone with software 3.0 or newer and open google.com/latitude
in Safari Mobile. At this time, the function is available to customers in USA, UK, Canada, Australia and New Zealand.
source: Official Google Mobile Blog