There are a couple of ANT + adapters for the iPhone for around $80 that can talk to all ANT devices and powermerters and record to any iPhone app that accepts that data, there are many. MapMyRide for instance. That said, I have yet to find a decent bar mount for my iPhone and the cost of iPhone replacement + short battery life makes a Garmin 500 or similar a better deal long term but more cost up front. Currently I am using a wired cyclometer w/ cadence + a cateye hrm for training. Not perfect, but cheap and accurate at all levels of "slow" and "suck" - so it works for me. For rides less than 3 hours I'll use TrailGuru to record my GPS tracks on my iPhone just for kicks.