Well I don't have I phone or IPad, but the wife always has hers. Its not used during our VFR flights. I have a friend who lost radio during a flight and it helped him out. He called tower and informed him as to the problem, solved the problem of landing at a controlled field without communications.
This is the major reason I chose a Bose A20 with BT (which has its own battery compartment even when connected to plane power, thus still working even when total plane power is off), for emergencies. Usually the mobile on RAM Mount next to the pilot is put to flight mode, but already coupled to the Bose, so in case COM fails it just takes one action to get the phone as backup communications channel.