Zlib Stream Compression is now in the trunk finally in the level that it can be considered "beta" or "testable".
The example in the above link uses the class org.igniterealtime.xiff.util.Zlib.
There also exists org.igniterealtime.xiff.util.ZlibNative that used the native Flash Player deflate/inflate methods. This however fails in compression with one byte, in comparison to as3zlib.
Please try out the "Zlib" version and reply in case you find any bugs.