Google's Android operating system is profitable for the company, according to Andy Rubin, Google's vice-president of engineering who is the co-founder of both Danger (acquired by Microsoft) and Android (acquired by Google).

In a talk at the Wall Street Journal's D:Mobilized event, Rubin told Kara Swisher and Walt Mossberg that "We're making money on the advertising that's generated through Android."

Mossberg asked: "Are you profitable if it was broken out as a separate business?"

Rubin: "Yes."

It's not clear quite how that would work, but the Android team is believed to be quite small - Rubin says that it began as eight people, but since that time "we have obviously staffed up". He admits (as we write today) that the original Google Nexus One failed because the US wouldn't tolerate a market where you bought a phone off the shelf and a product plan separately as you can in Europe. (Industry observers reckon it's more that Google didn't realise you'd need after-sales support.)

Rubin added: "There's no way I would have ever been profitable as a start-up. I probably wouldn't have made it as a separate company." (That's in contrast to Danger, which was sold to Microsoft for about $500m.)

He called Android the "Linux of phones" but said that didn't mean (to Swisher's question) that that meant it was "hard to get drivers for, only for geeks, no real consumer would buy it?" Rubin's response: "No, I think we've already proven that wrong. Bad analogy."

Rubin was quite complimentary about Apple and the iPhone, saying that developers have been finding it relatively easy recently to get apps approved, and that "My assumption is Apple is a company that learns from its mistakes."

He's less complimentary about Windows Phone 7, which he says has legacy code from Windows Mobile: "You just have this package of stuff that was invented before the Internet," Rubin says. "When the architects built that product, they didn't have the Internet in mind."

There's a hint that Rubin has spoken to Nokia - which would be remarkable - but there it is: "The company has new leadership [referring to CEO Stephen Elop]. They are evaluating lots of alternatives. I'm open-minded and a big proponent of Android." But he wouldn't talk about any meetings he may have had.

He also showed off a Motorola tablet prototype to show a forthcoming version of Google's mobile map application. Tablets, he thinks, are a new space: "we used to have PDAs, but the cellphone eventually replaced it. The tablet is a sort of in-between device so the use case is less clear. You might definitely have it on the couch, but maybe not on the subway."