Google Latitude is a service which allows you to see where your friends are and what they are up to then quickly contact them with SMS, IM, or a phone call. The service is already available for Android phones; however, Google is waiting for the iPhone 3.0 OS before launching on the iPhone.
Google has been waiting for the 3.0 software is because its not actually creating a native iPhone app for Latitude as all other location-based services on the iPhone are instead its using the Safari web browser to run Latitude. Thanks to HTML 5, Safari will be able to access a users location information and Latitude will be able to access that as well (provided the user gives permission). This will put it on par with what Google is doing in its browser for Android.
A web app doesn't seem like the best solution for Google Latitude on the iPhone but we will have to wait and see what happens.