John, I too only want to carry one and the iPhone seems the best choice. As long as it shows me on the correct road and close to the right elevations (my experiences with elevations has been much better with my 3Gs) I am happy.

I will be using a dedicated dyno hub to keep it charged on the Trike.

In the mean time since my 3Gs does not work with the new Wahoo Blu I will use the ANT, it also works with TrainerRoad sessions on my Kenetic trainer and that will be good as I train for the 2015 PBP.

By the time I get to PBP in 2015 the technology will have improved anyway. Thanks for your comments and help.

NOTE: does anybody know if the iPhone 4s requires a constant charge from an external battery or can it be charged directly from the dynamo? Thanks all.