if this is really what your wanting to do and you want to use a full router for your main network part might i sugest looking into this
it lists the routers and the phone they support for USB tethering
so you could get one of those listed routers a supported phone and use a phone as the modem and then a asus router as the router part, obviously this comes with an bit of an upfront cost but at the same time its the long term benefits,
this get around the only used in a phone situation as you will still be using the phone to tether and not an actually 3g/4g modem.
the one plan unlimited tethering for new customers ends on the 14th of july though so need to look quick in signing up and securing one as previous customers wont be effected by the new limit
<a href="http://www.thinkbroadband.com/speedtest/results.html?id=1401016123497593455"><img alt="My Broadband Speed Test" src="http://www.thinkbroadband.com/speedtest/button/1401016123497593455-mini.png" /></a>