Trouble is battery life. There have been a couple of hacks to do this.
Most of what it takes to make it happen is already built into windows
mobile.

But even when you get it working you're still going to see battery life drop
like an anvil once you start routing. Now, use a car adapter or a wall wart
and cradle and it's a bit less useless.

I've seen no tests yet as to throughput.

Oh, and you're also up against the handset's tendency to put itself into
standby mode.

Interesting in theory, a bit weak in actual practice.

-Bill Kearney