It's only my interpretation, but I believe Zen try to present their voice/FTTx bundles in a way that allows the pricing to be compared easily to BT Retail. The line rental cost appears under the headline broadband price, along with the one-off activation cost.
The voice line rental in a Zen bundle is of the same order as BT Retail line rental. The exact comparison depends on any line options - for example, Zen charge 90p/month for Caller Display, whereas you can often get Caller Display for free on a BT Retail residential line by signing up for 12 months of Privacy at Home with Caller Display.
Personally, I much prefer Zen's transparent pricing to BT Retail's "you can have this at a discount, but you recommit for 12 months, then the discount ends unless you make a further commitment" sort of pricing. I'm a long term Zen broadband customer, and recently moved both my lines to Zen (the line my FTTC service is delivered over and one other residential voice line). Zen don't have any of the "recommit for 12 months for a discount" nonsense and they have held their voice pricing for the remainder of the minimum period (12 months on the line with the FTTC, 1 month on the other line).
The only slightly disappointing thing was that moving my voice line to Zen started a new 12 month minimum period on the FTTC service, which was previously out of minimum contract period. I can understand Zen's reasoning: the voice and FTTC services are viewed as a bundle, also the FTTC service moved to a lower price on the same tariff to reflect the bundle discount. Nevertheless, I feel Zen's policy of starting a new minimum commitment on the FTTC service is a little harsh. As I have no intention of moving away from Zen and there is not really much they can do to improve an already unlimited tariff, it doesn't much bother me.
Since my connection moved to Zen backhaul network at the end of September, my Bandwidth Quality Monitor graphs have shown lower jitter and fewer latency spikes than on BT Wholesale backhaul. There was some initial instability whilst Zen presumably optimised the backhaul network (
8 October was one of the worst days), though this has disappeared in the past three weeks as can be seen from
my live BQM. Native IPv6 would be nice, but I know Zen have other priorities at present. I wouldn't be surprised if we see full LLU connections on exchanges where Zen have physical presence - I believe the Zen MSANs can take voice line cards.