IMHO i don't find there to be anything wrong with carrying a cell phone in an aircraft whilst flying. To an extent i do agree with KissMySquirrel with regards to the phone being a distraction which will draw you attention away from more important things. However, then again scrolling through the multitude of menus that feature on most modern gps' isn't going to help you see and be aware of what is going on outside the cockpit either.
Aviation is an industry where checking and double checking is encouraged; so for Martin1234 to use other means to cross check his position against his traditional navigation material, to me showed innitiative that should be encouraged. It would be a different story if he were have to called up his mate at the next waypoint to determine whether he could see if he was hovering over the right town.
Yes there is a risk the phone could fall into the pedal box and jam them, but then again, there is also a risk that the pen/pencil he writes on his map with could fall in the same spot with the same results.
As with phones in cars, if a phone in an aircraft is used in the correct manner, that is, in a cradle or linked into a hands free system or the like at the extreme end of the spectrum it can be the difference between spending a night injured beside a wrecked aircraft or waiting 20 minutes before you hear and EMS bird on site to winch you to safety.
It also means if you were to have a radio failure it gives you that extra line of communication, that can eleviate some of the panic some panic that may occur to an inexperienced flyer if this situation were to occur.