I can't for the life of me understand why you would sell the Garmin 76cs and rely on just an iphone! I would add the iphone for redundancy but never give up my Garmin.
I did not realize there was nav charts for the iphone but I am aware of charts and a program called Active Captain for Windows Mobile smart phones which I am looking into. I would not use a smart phone to replace my Garmin but instead use it to supplement my Garmin.
The smart phones of today are pretty awsome with Blackberry Storm and HTC Touch HD being strong competitors to the iphone. I am leaning towards the HTC with WM to run ActiveCaptain myself as I believe the AC program has more to offer.