I use the Chatterbox FRSX2.
It's capable of bike/passenger intercom, bike to bike, cellphone, mp3/ipod/whatever has a tiny plug, and an aux plug which would (I'd guess) work with a GPS.
The cell part... Mostly when I ride, I do so to get away from the distractions of life and have no need for a cellphone at that time. So I've never had it hooked up to the unit. If I NEED to use the cell, I'll do it when I decide to stop for a break.
The music part... I'm plenty happy enough with the music from my pipes.
The GPS part... I'll eventually find my way, even if that means taking the long way. One of my favorite says is, "With no destination in mind, you can never get lost" I usually pick a direction and go, not a destination.
The only reason I got this one is for bike to bike/passenger communication.
As opposed to some other units I looked at, it has an optional PTT (push to talk) button, which I have mounted on the handlebars. Runs on rechargable batteries or plugs into the bike (which also charges the batteries). Mounts to the helmet or (like I did) mounts to the bike, or in a pocket.
Also, many other units are not weather resistant like this one is.
This is kinda like the oil debate, many options to choose from, and many opinions on those options.
Look around, get opinions, and then you decide on which is the one you want.
Here is how I have mine mounted....
From riders view
And the PTT button....