In reply to ianstevens:
I have noticed on the occasions that have used my phone and my garmin that where inaccuracies have occurred there are clear deviations on the phone gpx file when overlaid on the os mapped position (and google earth sat pics) of paths.
The Garmin is not 100% either, but the aberrations appear more frequently and are larger on the phone (tell tale is straight lines jumping missed data points).
It's also worth noting that whilst chips maybe the same in higher spec phones, the way the output signals are processed makes a difference to accuracy (e.g. GPS walk compensation and calibration, behaviour on low satellite acquisition etc). The other difference is people tend not to put their expensive Iphone on your handlebars, and it's much harder to maintain a good signal from a pocket or bag.
Post edited at 19:36