Didn't mean to create confusion there, sorry - I thought the customer was calling their actual voice service "myvoice". You're correct in that myvoice is a "feature" (for lack of a better term) - it really is just a website that customers go to who have one of the EarthLink voice products - either EarthLink TrueVoice or EarthLink DSL and Home Phone Service. The myvoice website shows their current features, call history, etc.
Also - I know we're all about full disclosure here on DSLR, but I think you know what I meant when I said that there is no ATA "at the home". I don't think any customer cares that the ATA is actually the DSLAM.
It's just an easy way to differentiate between ETV (ATA at home) and DSL+HP (no ATA at home).
Anyway, my point is still valid. This call waiting issue can be fixed by having Covad change their SIP profile in their network. I haven't encountered any customer that this didn't resolve.