If you want HR, you're going to have to go Garmin. I don't think there are any HR straps that'll interface with an iPod.
I have a
Forerunner 305 with a handlebar mount. I get cadence, HR, speed, etc and can link it all to connect.garmin.com.
Plus, I've heard the battery life on an iPod.Phone isn't all that great when running a cycling app. The GPS feature uses a lot of juice from what I understand.
Also, the iPhone isn't waterproof, hardened against falls/drops, and allows you to receive calls/texts on the road ;P
If you're on a ride, and your phone comes off your bars and hits the ground at 20mph, how much would it cost to replace it vs replacing a Garmin?
Granted, if you want maps, you're up in the $450 (or whatever that would be in shillings) range.
https://buy.garmin.com/shop/shop.do?cID=160&pID=69043But you could get away with a 500 or the forerunner I linked above if you're not 100% needing of turn by turn navigation.