Maybe there's a solution to rural broadband by using the high-reliability frequencies reserved for voice purely for data — and using VoIP to make phone calls. http://www.networkperformancedaily.com/2008/05/can_voip_provide_the_solution.html

"Repurposing the broadband of 0-25kHz would result in... speeds of around 14.4 kBytes/s (or 115.9 kbits/s) upload and 28.8 kBytes/s (231.3 kbits/s) download. That's not much of a speed boost. Still, if you've been plodding along on a '56.6k' modem, at speeds of 7.2kBytes/s, this would be like an oasis in the desert. And what about those phone calls? Well, if you make the same phone calls with VoIP that you were with the standard 0-4kHz landline, it would only take about 20.8kbits/s using the G.723.1 codec — that still leaves you with 80% of your broadband capacity when on the phone — and 100% of your broadband when you're off it."

Why not use existing technology!!! IDSL is an ISDN-flavored DSL version. It uses the ISDN modulation to send bits over the wire, but with a full-time DSLAM connection as opposed to ISDN switched calling. It gets 144kbps - ISDN has two 64kbps B channels and a 16kbps D channel, and is typically used for a 128kbps bonded circuit. The big advantage of IDSL is distance - it typically gets about 30,000 feet, compared to about 18000 for most DSL flavors.