The ability for customers to keep their old phone number when switching to a new provider is proving a huge benefit to competition, according to figures from market newcomer 2degrees.

200,000 New Zealanders have ‘ported' their number to 2degrees since its launch two years ago, the company says.

Based on its most recent estimate of customer numbers, the 580,000 reported in March, around a third of 2degrees' customers have employed the porting service in making their switch.

Number porting was introduced in 2007.

2degrees CEO Eric Hertz says the results show mobile numbers no longer belong to the network, they belong to the customer.

"We understand that a customer's mobile number is part of their identity,” Hertz says, "and it should be portable, so they can take it with them, whoever they choose as their mobile provider.

Hertz adds that the porting is especially important for 2degrees given its launch to the business market in July.

"The last thing a business wants to do is change their number and risk losing contact with valuable customers.