TelstraClear is to offer its mobile services over the Vodafone network, after it was unable to reach an agreement to use Telecom's new XT mobile network before 2011.
The move comes two years after TelstraClear blamed Vodafone for the failure of its trial mobile network, Unplugged, and then switched to using Telecom's older network.
The Telecommunications Users Association says Telecom may be locking itself out of an important wholesale market with its latest decision to keep its new high-speed mobile network for its own customers.
Chief executive Ernie Newman says the new agreement is a sign of more competition to come. With three host networks to chose from, he says, it becomes a more attractive business proposition for other companies to come in.
Mr Newman says given the expected interest in wholesaling mobile networks, Telecom may be treading a fine line in its dealings with TelstraClear.
He says Telecom may have second thoughts if it sees too many more companies "hopping onto the Vodaphone network", as this will become a competitive area over the next two or three years.