Are DSL modems formatted and thus proprietary?

I ask this because I have a DSL modem kit that I am trying to sell. It was from Qwest so it makes me wonder if it was somehow formatted for just that ISP but on the other hand my guess is that DSL is DSL no matter who the provider is and that since it is probably just a box it will work with any ISP so long as it is DSL. How does this go? Is it all locked up and formatted only for Qwest or could this be used by anyone for whichever DSL provider they have?