Trustpower is to offer mobile phone services and wireless broadband through a wholesaling deal with Spark New Zealand.
The electricity, gas, phone and internet provider said it will work with Spark to develop the new products in coming months.
"Trustpower has been seeking access to mobile services for some time, and is delighted to have secured a wholesale supply arrangement with Spark," said Craig Neustroski, the firm's general manager for markets.
"Mobile is increasingly important to our customers, and the ability to offer it as part of our household services bundle is exciting."
Trustpower shares rose 2 cents to $6.44, taking their gain this year to 7 per cent.
The company has offered phone and internet services since 2007 and began offering gas in 2013 as part of a strategy to target more valuable customers and discourage them from changing supplier.
It had close to 400,000 customer connections at the end of September, and its more than 91,000 telco connections gave it the country's fourth-largest base of fixed-line internet services users.
Churn rates among customers taking power, gas and internet are roughly half those of customers taking electricity only. More than 102,000 take more than one service from the company.
Rival supplier Nova Energy last month started offering internet and mobile services. Contact Energy is also offering broadband, while telecom provider Vocus Group entered the power market two years ago.
Trustpower operates 19 hydro-electric schemes around the country and has a nationwide spread of customers to match. After Bay of Plenty, Auckland and Waikato, its next biggest regions for customers are Canterbury and Otago. It is the biggest retailer in Marlborough and on the West Coast.
Trustpower says many of its provincial and rural customers will not have access to fibre in the near future, which makes wireless broadband a great alternative.
Spark said it has invested heavily in its mobile network in recent years to increase both speed and capacity. It is available to just over 97 per cent of the population.
Spark wholesale leader Jilyut Wong said the company is planning to deliver hundreds more cell sites during the next few years to ensure service resilience and provide extra data capacity.