Using Google Analytics' Advanced Segmentation feature; you can now track your visitors from iPhone or iPod Touch. To enable the iPhone segment: click on the drop down menu, next to "Advanced Segments", and select "Visits from iPhones". You might want to turn off "All Visits" when viewing your iPhone segment; if the percentage of total visits to your site from the iPhone is small, it will be difficult to visualize the two sets on numbers on the same graph.
You can create a new segment for iPhone & Android: From Advanced Segments drop-down, click on "Create a new advanced segment", and create a segment with 2 criteria. Drag "Operating System" under the "Systems" dimension into the target area with the dotted-line border, and type "iPhone" into the "Value" field. Click "Add 'or' statement" to get a second target area, and do the same for Android. Then, you can name your segment "High-end mobile" and see that traffic in Analytics.