Ruphus: I also had VOIP setup on the HG659 with 2Talk this morning. I configured the router for ADSL and thought I'd have a go setting up VOIP. Followed my nose using the old HG556a as a reference and bingo. Worked fine. Now that I've been switched over to VDSL, it's no longer working.
Should have never worked with ADSL or VDSL with another providers VOIP. Its hard coded in to register solely to the Vodafone servers.