Can Verizon DSL and Comcast HSI get along?

Awhile back I had both DSL and Comcast cable in my office, and I tried setting up a failover route but it didn't work very well - the DSL slowed down the cable latency.

But that was on a linux machine, and I just found out Cisco has a router with both a RJ11 wan port for ADSLoPOTS (Asyncronous digital subscriber line over plain old telephone systems) and an RJ45 port for ethernet wan access. Interesting. I bet they manage the routing much better.