The Telecommunications Users Association says users could enjoy sharper deals for their fixed line phone and internet services if Vodafone buys TelstraClear.
Telstra is in talks with Vodafone about possibly selling its New Zealand arm.
Telecommunications Users Association chief executive Paul Brislen says a deal between the two could result in a powerful rival to Telecom.
Mr Brislen says that's particularly true in the fixed line area, where Telecom's dominance has not been seriously challenged.
IDC research manager Peter Wise says a takeover makes sense as TelstraClear's home phone and internet services will complement Vodafone's hold over the mobile phone market.
TelstraClear is also strong in the business sector and haS a large national fibre network which Vodafone could use to backhaul its own cellular network.
There are some overlaps in local loops, but a merging of the two companies networks would give Vodafone an much bigger network, possibly putting it on an even footing against Telecom, says Mr Wise.
There is speculation that Vodafone is interested in acquiring the high-speed 4G spectrum, required for high-speed mobile data services, which TelstraClear is expected to gain in the wake of the shift to digital television, a change due to get underway later this year.
Independent telecommunications analyst Paul Budde says Telstra has clearly signalled that New Zealand is not a priority.
Telecom shares fell 10.5 cents, 4%, to $2.435 each.