I am considering using Codename One for cross platform development, most immediately for iPhone, but subsequently for WinPho.
We already share a Java core across MIDP, BlackBerry, Android and Java SE/Swing, and would like to get rid of the need for separate development strands for C# and Objective C. About 65% of the Java code is shared, but that still means a complete port to a new Java API takes us around three months. That's a big spend to try out a new tool that might not pay off, while still having to maintain the other two code bases.
However, a set of classes that look like MIDP API classes but wrap the Codename One equivalents, would enable us to try out CN1 without too much expense, and, if it's successful, to make rapid transition, enabling us to stop developing other code bases and re-use the developers to make a "proper" CN1 port.
Such a compatibility layer doesn't exist... and it would probably take a similar amount of effort to develop it...
On the other hand... if other people face a similar problem, there is a chance to collaborate and share the cost.
I appreciate there will be many people who think this is folly, and that a native port is the only sensible way. However, given the current market size for WinPho, it would not be cost effective, and we would simply not support it at this time.
Anyone who would be willing to collaborate, probably on an open-source basis, and who has an existing commercial MIDP app (and so has a vested interest in the project's completion), feel free to post below!