Dunno about the iWorld phones, but I have tried just about every available GPS-Navigation app for my Android Galaxy Nexus smartphone, and they all suck hugely compared with the dedicated Garmin GPS unit.

The fonts are too small, the buttons microscopic, the voice prompts unclear, voice recognition non-existent, and the contrast too low. Not nearly as suitable for use while driving a vehicle. Otherwise fine.

And the in-car mount, power, and speaker systems for the phone are non-existent compared with the excellent dedicated setup for the GPS.

Oddly, Garmin do sell their software as an Android app, but only for Australia -- the app looks exactly like the dedicated GPS, with good fonts, voice, and buttons.

Note that I last looked into this about 6-months ago.

Cheers