ZK, a framework popular for Mobile Ajax, has added Comet support to their latest release.
ZK has supported server push since ZK 3.0, and ZK 3.5 now supports Comet-based server push. Developers simply use Comet in the way they are used to for normal Ajax development. The implementation of server push is transparent to developers. ZK chooses which implementation to use according to the edition of ZK automatically, but it is configurable.