The Commerce Commission has deferred its decision on whether the pricing of national mobile roaming services needs to be regulated.
Mobile roaming allows new entrants to use the networks of their established rivals while they build up their own network.
The commission says it is concerned that high prices will deter new entrants from challenging Vodafone and Telecom, and has given the phone companies three months to prove an investigation into further regulation is not needed.
New Zealand Communications, which is yet to offer phone services, has a commercial roaming agreement in place with Vodafone.
The commission is not convinced the agreement in itself will encourage more competition and lower prices for users.
It has written to the various players saying it will delay any decision about whether to carry out an investigation into regulating roaming prices, saying their actions over the next few months will determine the next step.
The commission says it wants to see whether access to national roaming services will be offered commercially on an industry-wide basis at prices that will encourage competition.
The competition regulator uses mobile termination prices as a proxy for mobile roaming prices, and in this area has not been impressed with voluntary offers by the dominant players to drop prices over time.
The Commerce Commission plans to release a draft report on termination rates in early- to mid-June.