Microsoft is spending $7.2 billion to acquire Nokia's devices and services unit in a move that's focused on the company's "One Microsoft" plan. Although the pair were already working closely on Windows Phone, it's clear there are some areas that could be improved. In an interview with CNET, Joe Belfiore — the head of Windows Phone product definition and design — has revealed that Nokia kept secrets from Microsoft.

"There are real-world examples of situations where Nokia was building a phone and keeping information about it secret from us," says Belfiore. Microsoft would prioritize its own software plans, not knowing exactly what Nokia was planning on the hardware side. "And then late in the cycle we'd find out and say, 'If we had known that we would have done this other thing differently and it would have turned out better!'"

Nokia left frustrated on occasions

While Belfiore doesn't cite any specific examples, it appears that the secrets were kept early on in the partnership between the two companies. Nokia and Microsoft worked closely together on the company's Lumia 1020, and Microsoft made core changes to its Windows Phone operating system as a result. Sources familiar with Microsoft's Windows Phone work have revealed to The Verge that Nokia was left frustrated by some Windows Phone restrictions on its Lumia 1020 camera software. Specifically, the restrictions made it difficult to store the large image files and make them easily accessible to phone owners.

These secrets and frustrations will no longer occur, and the collaboration appears to have helped Microsoft realize its priorities elsewhere. A Bluetooth file sharing feature is particularly popular in developing countries, but Microsoft wasn't aware as US consumers don't typically use it. "We didn't even have that feature, and we didn't even understand or appreciate the degree to which it was critical," says Belfiore.

Microsoft not worried about other Windows Phone partners

Microsoft's move to acquire Nokia is seen by many as a way to secure its Windows Phone future and a method to deliver on its devices and services promise. Nokia controls over 80 percent of the Windows Phone market, but Microsoft doesn't seem to be too concerned about other partners being upset at the acquisition. "Some of our partners have come, and some of them have gone over the years," says Belfiore. "It's not likely to change the big picture." With Nokia on board, Microsoft now wants to triple its Windows Phone marketshare by 2018.