Right now e-mail is completely based on the customer. The few customers we have are businesses that already had servers in place and run their own e-mail. We do all static IPs, so it's never a problem with DNS or anything.
There are a couple of individuals that are signed up, but they are "prosumers" that either run their own servers, or wouldn't use an ISP e-mail address anyway.
We plan to eventually have a mailserver up for our customers, but since we haven't been doing a lot of hookups to the public yet, it's not at the top of the priority list. Most of the people we hooked up are already clients in another respect, and this is just another part of their service contract or added to their billings.
The could tell what the actual telco is I suppose if they looked closely at their online account that's tied to their telephone line (at least in the case of Qwest customers), because it shows the "actual" ISP that they are with, but since the ISP itself doesn't offer DSL under their main name, going to the site wouldn't really get them a lot of info anyhow.
We originally set up all the contracts with the ISP to do small DSL-connected WANs, but figured we may as well provide DSL to some of our customers too since we could. Since we are managing the connections more closely than a random ISP would... i.e. we run thier servers/networks as well, we don't really need to have services in place just yet like Covad/Speakeasy/Whatever ISP would.