if you take a look at this page about leopard server they have a brief snippet about IDLE support
the important bit isn't the server supporting IDLE, but that they make the distinction that only leopard users get IDLE support. i believe iphone, if not complete based on leopard, certainly has lots of leopard DNA in it (core animation, quick look, etc...).
i know IDLE is specifically push, but from an end user experience it's almost identical.
Mail services
For fast email access while on the go, Leopard Server supports IMAP IDLE to notify Leopard users immediately when new email arrives. For enhanced mail service reliability and scalability, Leopard Server supports Active/Active clustering when used with Xsan.
the important bit isn't the server supporting IDLE, but that they make the distinction that only leopard users get IDLE support. i believe iphone, if not complete based on leopard, certainly has lots of leopard DNA in it (core animation, quick look, etc...).
i know IDLE is specifically push, but from an end user experience it's almost identical.