The companies charge one another 17c a minute to connect a rival firm's customer to one of their phones - a fee that is then passed directly to the caller.
Yesterday, the Commerce Commission advised the Government to regulate the charge, and suggested it could go as low as 4c a minute.
Although there is still a submission process before Communications Minister Steven Joyce approves the change, it is widely expected he will do so.
New Zealand and Mexico are the only countries in the OECD that do not control the rate mobile companies charge one another.
The chief executive of 2degrees, Bill McCabe, said if the Government regulated, it would create greater competition.
"All consumers will benefit from this. They will benefit from a ferociously competitive market."
On Tuesday, 2degrees announced it was dropping voice calls from 44c to 30c a minute for pre-pay customers.
This price includes the 17c cross-network fee.
This could drop by another 13c if Vodafone and Telecom dropped their prices as well.
If the rate were dropped to 4c a minute, it would finally bring New Zealand in line with international practices, Mr McCabe said.
Consumer NZ chief executive Suzanne Chetwin said the Commerce Commission announcement was good news for New Zealanders and the result was what the organisation had been pushing for.
"There are four million mobile phone customers; this will create innovation in the market. It means the cosy duopoly is over."
The Commerce Commission backtracked on its earlier recommendations in April, after Vodafone launched its Talk plan.
This favoured its own network by pushing prices down as low as 6c a minute to call other Vodafone customers.
Ms Chetwin said the Talk campaign was anti-competitive and a clear illustration of why Consumer NZ had fought for regulation.
The minister will make his decision after submissions close.
