There are a few options which you can use, and all of them are homegrown ones (available from PTCL).
The first is to use a PTCL Evo Tab. This can replace your touch screen music player / video player / mp3 player, when you connect it to your deck / amplifier, etc. Having this in the car obviously removes the need for any other device, since you have Viber, Sygic, various GPS programmes and basically anything you need to have, on an android device. In addition, it can create a Wifi Hotspot that is good for 5 devices. The downside to this is the battery time. Which is NOT good at all. If you keep it continuously charged (ie, keep it connected to a USB source) it works just fine.
PTCL Evo 3G Nitro comes up next. This is a high speed wireless device which creates a Wifi Hotspot good for 5 devices. It's fast, has great connectivity and is small and unobtrusive. Can easily fit in the car's glove compartment, and when you're done in the car, simply put it into your pocket and remain connected even when you're not travelling. Can be charged from any USB device (present in most decks, nowadays). Decent battery time, as well (3-4 hours of continuous use).
Next up is PTCL Evo Cloud. A small device that is almost identical to the Nitro, but less "speedy". Has much less battery time, too.
PTCL Wingle connects to any USB output (like in most decks) and creates a hotspot for 5 devices. The obvious downside is, that when you step out of the car you won't have connectivity, until such time as you connect the Wingle to a USB source.
Bottom Line: The Nitro. It's quick, portable, has good battery time, and can be hidden anywhere you want to. Of course, if you want to go about installing a router / modem device just for the challenge, and for the sake of shi*s and giggles...that's obviously your choice.
Best of luck.