Mushroom Networks sells a trademarked broadband bonding device. It goes on the client side not the DSLAM side. Here's the official description:
The first product offering of Mushroom Networks using the Broadband Bonding® technology is the TRUFFLE Broadband Bonding Network Appliance (BBNA). The TRUFFLE BBNA6401 is a standalone product designed for a small and medium sized business (SMB) that implements aggregation of multiple Internet access resources, for example, multiple DSL lines, cable modems, T1 access lines, etc.
I don't know anyone using it. I don't even know how viable it is. I ran across it when I saw a press release for $200 T1 bonding.