There are a lot of threads on the topic and the field is split pretty even. I use an iPhone 4 and don’t have any other devices electronic except a few methods to be able to recharge the phone on the road. The major drawbacks to the phone will be battery life (charging) ability to see the screen in bright light (GPS units are better) and being not hardened to the elements (GPS units are) The iPhone on the other hand is also a phone a camera and a camcorder, a fairly powerful personal computer for internet use, I have over 3000 songs on mine, it will give you weather warnings, it can be used as a eReader holding books, it plays games if that’s your idle time thing. And about a million other apps that you may find handy to have around such as going on BikeForum and asking questions. I had mine mounted to my bars for a year and came to the conclusion it doesn’t do me or the iPhone any good being there. The combination of sun and a distraction I now keep it inside my top flap on my bar bag. Out of the elements and not being banged around as much. I find its just as easy to pull over and put my reading glasses on and access the mapping take a call or whatever else I need to do. The battery lasts much longer if I’m not keeping the display on watching my inch by inch progress. It’s also easier to see if it’s shielded a little by the cover. Some people have all 3 with them but if I have to have just one I like the iPhone idea. Others will tell you otherwise. If you go with the phone method then come back and ask or search there are 100 of posts talking about bike and mapping apps and also charging methods.