(CNN) -- Microsoft's purchase of Nokia's mobile phone business will allow the company to compete against "big established players" by being "agile and clear" with the consumer and with its innovations, its outgoing chief executive Steve Ballmer has told CNN.
The deal, announced late Monday night, pits Microsoft squarely against Apple and Google in the hotly-contested smartphone arena. The $7.2 billion purchase gives Microsoft control of the second-largest mobile phone manufacturer in the world, according to IDC.
Ballmer, in an interview with CNN, said: "The dynamics of really competing in this market against big established players means that we're going to have to be absolutely as agile and clear with the consumer, agile in our innovation, agile in our business decision making."
The two companies have been in partnership since 2011, when Nokia moved away from its homemade Symbian smartphone operating system and replaced it with Microsoft's Windows Phone.
Of the existing deal, Ballmer said: "Despite the close cooperation and great work we've done together we see the opportunity to, none the less, move faster and accelerate and take market share."
The best way to do that, he said, is to be: "One company making one set of decisions."
Nokia has been troubled, and while sales of its top-end Lumia smartphones are growing fast, they remain in the shadows of the iPhone, Samsung Galaxy S4 and even Google's new Moto X.
Nokia has been led for the past three years by Stephen Elop, a former Microsoft executive. Elop stepped down as Nokia's CEO on Monday to become the head of the company's devices and services business. He will continue leading Nokia's phones business as the devices chief at Microsoft.
Elop has been widely named as a potential replacement for Ballmer as Microsoft's next CEO. When asked if Elop was a natural successor for the role, Ballmer said the board was going through an "open succession" process to consider internal and external candidates and would continue to do "its proper job in considering candidates to be next CEO of Microsoft."
But Ballmer said he was "not finished ... I'm running very hard until we do have a CEO successor."
The deal, Ballmer added, was the biggest he had done at Microsoft, and "it's part of what I would call probably the most significant transformation of the company.
"I am excited, I am excited to welcome the now 32,000 Nokia people who will be joining the Microsoft family."
CNN's Jim Boulden, Irene Chapple and CNNMoney contributed to this report