It's an option as their fibre goes past - I think the major problem is that the ISP's that connect to unison no one has ever heard of and none of them publish their plans on their website and I have to say I'd be concerned about the amount of international bandwidth they buy.
I couldn't comment on that - however as far as national players go, both FX and CallPlus are interconnected in Rotorua (although the website only says Hawkes Bay).