How to hack airport extreme to support USB 3G modem? [closed]
I am not aware of any firmware for the modern Airport base stations other than the official Apple ones. Adding support for new types of hardware sounds rather ambitious, so I'd expect it to follow simpler tweaks like adjusting the signal strength.
Others may have better info, though.
Another idea is to turn internet sharing on in the computer to which you connect your 3G USB modem. This way you convert your mac into a router itself rather than buying an additional router. I have this set-up for my temporary location and it works like a charm...