The routers in terms of 3G are useful as they provide the connectors for fitting better antennas too, and in a vehicle situation this can be important.

The router does NOT improve the signal it is the antenna it is connected to.

A 1 cm x 1cm router will be as good as one the size of a van. The antenna and quality of cable connecting the two are all important

FYI - You might find this recent blog entry from AAISP's RevK about 'IPv6 BMW'
http://revk.www.me.uk/2011/10/ipv6-bmw.html

In reply to a post by TheHappyDuck:

I understand but will a router have a larger range and less drops than a dongle as it is larger and you can add an Antenna?

You almost certainly want a "MiFi" type unit that isn't locked to a single network. Then you can put in a SIM card from the network with coverage where you are. Don't forget that many rural places don't have 3G on any network. North Scotland being one I have knowledge of. (2G on Vodafone is very comprehensive, but no 3G).

If you're near the motorways most networks will have 3G tho.

Depending on throughput I've seen 7meg download and 1.8meg upload on my new 3 HSPA+ MiFi unit - but most of the time its doing around 2meg download and 0.8meg upload.