Re: And what about the people ...
Or the people that have a mobile phone that is just a phone.
A good example would be my father who sticks with his Nokia 6310 for it's 2 week battery life and ability to use an external aerial.
The external aerial bit is important as he spends a lot of time living on canal boats (and mobiles don't work too well in steel boxes).
Being boat based also brings up another problem with the proposed app, He has no postcode or address (when I ask him where he is I usually get the name of the canal he is on and the bridge / lock numbers that he is between)