I played with the Sun Wireless Toolkit 2.5 a little and it seem to have quite a few improvements since I last tested it (of course extensive API support, new emulator skins, more polished UI, etc.) although it is still lacking authroing tools (well, that is what NetBeans is for, right?)

Now a word of caution. I noticed that the default build settings for the API support is MSA. If you are building an application to be used on real devices, make sure to change this setting. The problem is that the MSA requires MIDP 2.1, which is not yet available on the real handsets. You can change this setting either by choosing Custom API selection, which allows you to freely select the required APIs, or then by selecting JTWI from the drop down menu.

If you do not change this setting, you cannot install you application on any real phone, as the device complains about incompatible versions, or something along those lines.

This reminds me similar problems with devices supporting only CLDC 1.0 (including S60 2nd Edition and 2nd Edition FP1 phones).

Lesson learned: If you have problems on getting you MIDlet even installed on your device, please check first the build settings for the project. (and secondly, make sure all the JAD and Manifest entries are correct...)