You could try the iTransmogrify bookmarklet for the iPhone to get Flash to work on the iPhone.

Apple has more or less stated that Flash will never happen on the iPhone due to some technical reasons. Also, Apple did not include Java in the iPhone SDK, nor does its license really allow someone else to port the Java runtime (even though Sun said they would do it anyway).  So at this point the only two options are a web-based (css/js) client or someone start over from scratch with Objective C.  I don't think the Later of those options will happen any time soon for Spark, but the web-based client did exist for a while (buggy as it was), so that might be a real possibility.

The major issue stopping us from doing an iPhone client is the restrictions on background processes. Signing out every time you switched apps would suck. ]]>

That applies to us too, plus the lack of Flash and Java.

iPhone 2.0 has some "push" messaging abilities, which should make it possible.  Need to sign NDA's to get the full SDK and specs on it, but it should be possible to write an IM client using that framework.  But, it would need to be written using C/ObjectiveC I assume, so none of the existing Spark/Smack/etc API would be useful; and additionally I think there are some license incompatibilities with GPL stuff, making it even more challenging. Im sure someone will come up with one at some point, but I dont know if the Jive folks have the resources to devote to that right now.