Google Latitude for iPhone and iPod touch is a web application that runs on iPhone's Safari browser. Now you can share your location with your friends, as well as control who gets to see it, all from your iPhone. You'll also find basic Search and Directions functionality to help you get around the world. And just like Google Maps for mobile client apps, you can press the "blue dot" to be taken to your approximate current location on the map with My Location, thanks to Safari now supporting the W3C Geolocation API. To start using Latitude, go to google.com/latitude from the iPhone's browser. You can even add a bookmark to your home screen for one-touch access.
More info: Mobile Blog