Vodafone's $840 million purchase of TelstraClear has prompted the regulator to start monitoring fixed line calls to mobile phones.
The Commerce Commission already monitors the cost of calling others on a rival mobile phone network, after regulating to slash the cost of switching phone calls and text messages between rival networks last year.
The commission found the merger of Vodafone and TelstraClear would not substantially lessen competition.
Even so, Telecommunications Commissioner Stephen Gale says, the merger is a major change in the industry and the regulator plans to observe its impact on fixed and mobile pricing - separately and in bundles - and monitor any changes.
Dr Gale is not anticipating any anti-competitive pricing arrangements coming from the newly merged entity.