I have a plain jane cell phone that I carry on the bike, but it's turned off most of the time. Came in handy on Saturday when I helped out a downed rider. The only other cell phone on the scene had problems getting a signal, but my phone worked.
The only thing on my bike to carry anything most of the time is a little tool roll. By the time I stick a bottle of water in it, there isn't any room for much more so a camera built into the cell phone would be nice to have...especially when you're at a bikini bike wash like I was Saturday afternoon.
