I use both, a Garmin 500 and iPhone4 with cyclemeter. Without exception the iPhone records speed and elevation less than the Garmin. The Garmin doesn't have cyclemeters email alerts - you can set it to send a recipient list regular updates as you ride. I have those kind of features turned off when I ride, so I have no problem with battery life. I did a 200km ride, seven and a half hours, and the phone didn't go flat. The Garmin is a better training tool, but if you don't need cadence/heart rate the iPhone with cyclometer is a good chice. I find cyclemeter to be a very good programme, with plenty of features and report options such as comparisons, best-worst-average, and is handy way to show your mates where you've been riding.