Ballmer was participating in a Mobile World Congress panel discussion on the "open mobile ecosystem", alongside Nokia chief Olli-Pekka Kallasvuo and AT&T head Ralph de la Vega, who used the occasion to inadvertently announce Dell's imminent smartphone.
"Open means different things to different people," Ballmer said. "To some people, open means open source. It means more than that and different than that to me. Open can mean an open platform that people can extend, or it can mean open standards that are baked in. Ultimately the companies that succeed will be open, maybe in different ways and at different times."
To Ballmer, "open" refers to "the power and success of the partner ecosystem approach [that Microsoft] pioneered at the beginning of the PC revolution".
"The industry makes about $18 for every $1 Microsoft makes through the Windows platform," he said.
"We had to strike a pragmatic balance between a very unstructured openness in which privacy and security are difficult to control, and the other end [where there is] much less choice, less flexibility but often less chaos and many fewer problems."
"In the mobile space, the proportion of revenue that goes to the ecosystem is even higher than that in the PC ecosystem," Ballmer continued. "This is the right approach. We support open networks, open competition and open access . We've doubled down on the level of interoperability that you see in our PC ecosystems."
Then came a spot of iPhone-related complaining, with de la Vega claiming Apple's handset would be even more successful "if there was commonality about where the applications could work".
"The iPhone has a nice app platform," Ballmer said. "People are downloading. But most of these are really front-ends to websites."
Microsoft announced its own mobile application marketplace on Monday, although details remain sketchy.
Ballmer then pointed out that, with the iPhone, "you can only get it from one hardware maker, with their choices and their price points". He contrasted this with the approach of Windows Mobile and Symbian, both of which allow the operating system to run on a variety of different handsets.
This article was originally posted on ZDNet.co.uk.