Yes, you can, you can also get two lines from the same company, but you do need two physical phone lines.
Jack's link mentions cheap load balancing routers at the bottom of the page. You will not be twice as fast, but you will be able to download twice as much.
Also, it may be load balanced per PC so a single PC might not see load balancing benefits. (may depend on router)
Is there a load balancing router that can auto switch from one connection to another if it fails. Specifically, I want it to maintain a secure VPN connection. But if the currently used connection fails, I loose everything. The router does switch to the new connection, but I still have to reconnect with all my software which defeats the purpose of load balancing. The obvious issue is the secure tunnel as it can't be easy to clone. Would a dedicated VPN router be able to start VPN connections with both connections and seamlessly switch if one fails?
Thanks