I bought a myfi about a month ago, it worked great in the car with the external antenna.
elsewhere though.. not so good. on the commercials they show people indoors listening to it. BS - unless you've got a long antenna running to the nearest window. that's why it comes with antennas for everything. you've got one for the car, house, even one to hook to your shirt.
i tried mine without the external antenna everywhere. sitting right under the windshield on the airplane (where you'd think it'd get a good signal), in the backyard, even on the beach with nothing between the reciever and the sattelite except sky. it didn't stay locked on enough to even listen to.
i wanted it mainly for flying, and maybe i just got a bad unit, but it was kindof a dissapointment. i thought it'd work good enough to walk around outside and not need antenna wires hooked up to it.
so i took it back yesterday and got the 4GB ipod which is $100 cheaper.