I've got a Garmin 2955 to handle navigation, which isn't dependent on being "in range" of a cell tower. It does all the things you mention plus I can just talk to it instead of playing with a touch-screen or iDrive controller.
The problem with the onboard NAV system is that it's too expensive to start with and the updates are costly and infrequent. If they'd cut the price in half and provide at least quarterly updates to the maps plus traffic alerts at no extra cost, now THAT would be something I'd buy.
2013 F30 335i M-Sport 8AT/MPE/MPPK, 2011 128i M-sport Cabrio 6MT/PE