DSL.net which is now part of MegaPath deserves a special mention on these pages because it appears that they are the last major SDSL provider who operates Copper Mountain DSLAMs. We haven't been able to find out the exact extent of the old DSL.net service footprint, but it is based primarily on the Atlantic Coast and does not unfortunately cover the rest of the USA-occupied continent.
When providing SDSL service in geographical areas not covered by their CM-based DSL.net footprint, MegaPath goes through Covad like most ISPs.
We have someone from MegaPath on our project's mailing list, so if anyone is interested in MegaPath's services or in open source connectivity to such, please post on our list and we will probably be able to give you a better experience than with any other ISP. If MegaPath's DSL.net CM DSLAMs are still in service by the time we finally finish building our OSDCU, we'll have some fun!