KEY POINTS:
A woman's half-hour "free" call from her mobile to her friend's one has cost almost $50.
Vodafone customer Emma Cooper was charged $49.71 after calling a friend on an 021 number - a call she thought was free. But she was unaware that her friend had switched to the Telecom network under the "number portability" plan.
Vodafone head of communications Alison Sykora said her company had publicised the changes involved in portability, but it was ultimately the responsibility of phone owners to tell friends of their switch.
Ms Cooper believes phone companies have not done enough to prevent expensive mistakes like hers.
She said one of the networks should have informed her before connecting the call that she would be charged differently.
It was unreasonable to expect her friend to let her know.
"I very rarely call Telecom numbers because it costs me more on my plan, and I would never have spoken for this long, or at all, had I known how much it would be."
Ms Cooper said she "was not at all happy" and had written to the Commerce Commission.
Number portability was introduced in April, allowing phone and mobile users to switch phone companies and take their number with them. By August, 35,000 New Zealand customers had switched phone companies.
The telecommunications industry is understood to have spent $100 million preparing systems to handle number portability.
Ms Sykora told the Herald that it was the first complaint she had heard regarding portability, and believed Ms Cooper's problem was an isolated one.
Telecom public relations manager Rebecca Earl said her firm recommended that people inform their contacts when they changed phone companies.
She also said that users should note in their address book which network their contacts belonged to. No Telecom customers had found surprises on their bills as a result of number portability.
Telecom and Vodafone customers can find out which network someone belonged to by texting their number to 300.
