Here’s a great resource for working with maps on the iPhone: http://code.google.com/p/iphone-google-maps-component/
This code will allow you to add maps which are interactive including panning and zooming. Also, you can determine the location the user tapped on by pixel x/y or lat/long!
You can also add overlays for markers including customer markers. Based on tap events on markers, you can then display details, etc. Very cool stuff. Very useful.