Connecting to a mobile internet provider from an ethernet router

I have fallen out with my cable internet server provider, and I now want to replace my cable connection with mobile broadband.

I am thinking of using Orange, or possibly another provider, but they all seem to provide a USB stick which probably will not operate properly on my open source based platform.

My computers use ethernet, and I have an ethernet based router which connects to the cable modem. I want to basically remove the cable modem, and place some sort of mobile router device that will either connect directly to the mobile provider, or will accomodate one of the USB sticks to connect to the provider.

The connection coming from my router will be ethernet, so my setup will look something like this:

computer -ethernet- firewall -ethernet- router -ethernet- mobile broadband

Is there a suitable device that will allow me to connect via tcp/ip ethernet to a mobile broadband provider?

I have no wireless access devices nearby, so this needs to be a true mobile broadband connection.

Will they work with any provider?

I am in the United Kingdom of Great Britain, so I need something that can be used with broadband providers here.

(Orange, O2, Vodaphone, 3, etc.)

There are routers that you can put an air card into and access 3G services . They're pricey, but they're out there.

Are there any 4G providers over there yet? If there are, they may provide an alternative as well. Here in the US, there are a couple of Internet providers that provide 4G service via a home modem without having to resort to a USB modem.