Can you build an iPhone app which has 2.1 as it's target SDK, but uses 3.0 features?

Question

I noticed that IM+ came out today and lists it's minimum requirements (in iTunes) as OS 2.2 or later, but they support 3.0 features like push.

Is it possible to build an app (eg: one binary) for firmware 2.1 that has features like push (or SMS or whatever) that are only enabled on phones with the 3.0 firmware? It seems like it is, but I have no idea how to do it.

Answer 1

I guess this has been answered before.