Actually this thing is not entirley new and such tools already exist: there are enough arduino-style boards out there that allow you to create a phone already,

Actually this thing is not entirley new and such tools already exist: there are enough arduino-style boards out there that allow you to create a phone already, as well as a bunch of other useful things: get a gps modules, a gprs module, a keyboard module and a screen module and off you go.