This was posted yesterday:

Probably you have heard the exciting announcements made at the Symbian Smartphone Show on 21 October, 2008. We at Sony Ericsson Developer World are excited about what this will mean for our developer community.

From all the news coming now about this, I think that there are a question that are most important for you as third-party developers. I will try to answer it here.

Which software platform will Sony Ericsson base their Open phones on in the future and hence which SDK should you as a third-party developer base your development on? The straightforward answer is the Symbian Foundation platform where we are a founding member of the foundation. But as you all know the Symbian Foundation is not a reality yet and you probably want to know which SDK to use and what to convert your UIQ apps to. In the meantime, you should use Symbian/S60 5th edition as this will be compatible with the upcoming Symbian Foundation platform.

As you all know we cannot communicate anything about upcoming products. But we are committed to giving you the information as soon as we can, so please tune in to Developer World from time to time to check for the latest news.

We hope these answers will give you some peace of mind so you could focus on the great apps that we know you can create!

In case of applications for the G700/G900 and older SymbianOS based phones the UIQ developer site offers the latest SDK material:
http://developer.uiq.com/