Telecom slumped 23.5 cents (8.53%) to a share price of $2.52 on Friday after its profits came in slightly under market expectations.
Telecom has lost nearly 400,000 mobile customers.
Though it posted a 9% lift in full-year underlying profit to $422 million, much of this lift was due to cost cutting as its revenues fell 9% to $4.5 billion, and suffered a 19% drop in mobile customers.
Closure of its former CDMA network earlier this year required some of its customers to switch to a new network and some chose to go to rival providers rather than Telecom's new XT network. Telecom's mobile customers dropped from 1.98 million to 1.6m this year.
Acting chief executive Chris Quinn says most of those "lost" clients were low-paying, or low usage customers.
And he says the average ARPU (amount spent per customer) lifted 9% to $35, and he believes this will keep growing.
But calling revenue is down 9%, as customers use online messaging systems such as Skype - and he says the company is focusing on building its fibre, broadband and data revenues.
New chief executive Simon Moutter has only been in the role for two weeks, but says he has ambitious plans for the company.
Telecom will pay its shareholders a dividend of 11 cents a share.
Forsyth Barr analyst Guy Hallwright says the company's flat outlook for this year and a pause in the proposed share buyback, also appears to have disappointed investors.
Last year Telecom spun off its network arm to form the standalone listed company Chorus, which Telecom had to do in order to participate in the Government's ultra fast broadband initiative.
The share price for Chorus also fell, dropping 6 cents to $3.16.
