BNZ has renewed its contract with Vodafone and TelstaClear for another six years.
The bank and telcos signed a "significant contract" on Friday that covers network and related services, calling, security services, customer contact centre, enterprise video and voice services, managed services and professional services.
"This is a milestone partnership however you look at it," said Vodafone chief executive Russell Stanners.
"There are very few major organisations that have developed the mutual trust and expertise to work together so productively for so long," Stanners said.
The contract extends a relationship between that began in 2002 for another six years.
Vodafone got the green light in October for its $840m takeover of TelstraClear andthe two companies will merge their operations under the Vodafone banner within the next 18 months.