Is it possible to combine the bandwidth from a DSL modem and a ClearWire modem?

Solution 1:

You would need an outbound load-balancing router. pfSense is a free router package that you can run on an extra computer if you have one lying around.

This will not magically double your speed, but it will double your bandwidth. All of your connections will still go at 4-5Mbps, but you'll be able to have two connections running at 4-5Mbps at the same time. You could separate them manually by computer or something, but the advantage of a load-balancing router is it'll select the uplink that has the most available bandwdith. You can also set it to use one as a backup in case one fails, and automatically switch as soon as that's the case.

For the biggest improvements, make sure your web browser supports http-pipelining and has it enabled.

Solution 2:

You would need to bond your internet connections. But this would not double your speed due to the way the tcp/ip protocol works. It would single out one of the isp's for say a download. What this would do is what you already stated be a redundant line.