The Telecommunications Users Association says a lot of companies that rely on the copper network to deliver their services aren't ready for the fibre world.
Telecom launched its ultra-fast broadband (UFB) packages last week but is retaining its existing copper-based phone lines to service voice, monitored alarms, faxes, EFTPOS, SkyTV and medical alarms.
Telecommunications Users Association of New Zealand (TUANZ) chief executive Paul Brislen says all the UFB providers are selling voice and data over fibre except for Telecom.
He says Telecom has done this for two possible reasons - one to ease the pressure on networks company Chorus and the other because their own systems aren't yet capable of offering a voice over fibre service.
"So they've done it as this halfway measure in order to ease the transition for customers," Mr Brislen says.
"A lot of the burglar alarm companies, a lot of medical alarm companies, if you've got Sky TV, they quite often connect via copper line as well. None of these companies seem terribly ready for the fibre world.
"And so in order to keep them on board, make sure that nothing dramatic happens to your home phone while this process is going on; they've taken this hybrid approach which hopefully will mean that customers don't ever have that terrible moment where the technicians say, 'Well we've cut off your old service and we can't connect the new one and we're all going home now and we'll see you in the morning'."
Telecom says it is looking to introduce a voice over fibre product later this year.