Lots of people are suggesting it will involve Nokia using the Windows Phone 7 OS in some of their smartphones.
As someone who is developing applications for the WP7 platform I would see this as a really good thing. To potentially have many more potential users of the platform would be great.
I have one big concern though: that Nokia use a custom version or fork of WP7 and not the same one as everyone else. This could lead to all sorts of issues that would affect developers, users and the platform. As a developer it's amazingly reassuring to know that if an application runs on one device it will run on all of them. This leads (well it should do) to much higher quality apps, which in turn should lead to happier users. I really don't want to go back to a world of fragmentaion on what we've told should be a single platform.
To be clear, no-one has suggested this as a likely option (AFAIK), and the Nokia using WP7 is still just a rumour, it's just I thought of it-for some reason-and it scared me.
I REALLY hope this doesn't happen. :)