Telecom's cable network has been available for wholesale to other ISP's for many years now and there are a handful of ISP's who do resell cable plans.
As for TCL not having to make their phone service available it's essentially the scope of what the whole Telecom ULL and wholesale regulation was designed for. It was to force Telecom to wholesale their network and offer incentives for other players to enter the marketplace, not force new players who do build a network (such as TCL, Econet, BCL/Kordia) to also offer their network at wholesale rates to other players.
In some ways it's a moot point anyway, within a few years you'll have a large number of people using VoIP as their primary phone and most providers will be offering a dual play voice & internet service using a naked ADSL circuit (whether it be via Telecom wholesale or their own DSLAM) and VOIP. There is nothing stopping any ISP out there entering the Wellington and Chch markets reselling TCL cable plans and their own VoIP service.
The key differences between TCL and Telecom is that Telecom owns the last mile to most homes in the country. That is their edge. TCL only connect the last mile when a customer signs up. So even there were a way for TCL to open up access to their network to other players, for many customers, the other player would have to pay for the final connection to the home. There would be no point for the other player to try to use TCL's infrastructure to an existing customer premises for their own services - they just could not be competitive enough.