"The search engine has been heavily integrated into the OS, so it would be hard to offer an alternative", Greg Sullivan, senior product manager for Microsoft told Pocket-lint in a one-to-one briefing.
While Sullivan has said that Microsoft would allow other search engines to create an app, or even, presumably, a hub, it has confirmed that it will not be letting any other company (read Google), be the default search engine for the new phone operating system.
The move is in stark contrast to Apple's iOS 4, which has actually just added Bing and Yahoo alongside Google for its users to search the web.
One of the key reasons for the decision is the "Tell me" integration, explains Sullivan, that will allow users to press a button and then speak to the phone giving it voice commands to search not only the phone, but also the web.
It's a system that aims to emulate Google's voice recognition search feature on the Nexus One, or Apple's Voice Control, which gives you the ability to give vocal instructions to your phone.
Sullivan showed us the feature working in two instances during a demo on the company's developer preview device. The first was where he asked for details on his flight back to the US and the other where he was searching for something in his calendar.
Microsoft is clearly hoping that Windows Phone 7 users will help boost Bing's awareness and therefore market share - something that it is already doing quite nicely on its own, according to the latest figures from the US.
What do you think about the decision to only use Microsoft's Bing for search with the phone? Is it a deal breaker, or a total put-off? Let us know in the comments below...