Currently I'm using only the iPhone's internal resources and so I am not measuring heart rate, cadence or power. I use a program called cyclemeter (available on the iOS store), that is very, very comprehensive. I've found it to be completely reliable thus far. It amazes me just how sophisticated these programs for iOS have become. I am thinking of trying this accessory however, Wahoo Bike Pack, which is an example of what can be implemented on the iPhone and includes a 'water resistant' case and ANT+ connectivity.
All the best.
Hmm.. Fancy way of Wells Fargo saying "Give Us More Moneyz".