Most cellular modems are USB devices, intended to be plugged into (laptop) computers.
You should be able to use something like the awesome ASUS WL-330N3G credit-card sized 3G router (http://www.asus.com/Networks/Wireless_Routers/WL330N3G/), once 4G-capable versions become available. Which I really hope they will.
Of course, you could also replace your router with a 4G USB-capable one.