I've recently got a solstice and I've been looking at the API also.
It looks like you have to use the java MIDP/CLDC api to write applications. I haven't found any non-java solutions. The widgets seem to use a separate API, I think it's called touchwiz.
If you're a java programmer, I think you'll want to look at the MIDP/CLDC documentation. This page could also be helpful to determine the specific subsystems you can use:
http://stats.getjar.com/device/Samsung/SGH_A887_SolsticeI'm pretty new to this too, so correct me if I'm wrong.
