iIrssi is currently under development. When complete, it will let you receive notifications from irssi on your iPhone or Mac OS X machine through Growl and iPhone push notifications. I do intend to charge a nominal fee ($0.99, probably) for the iPhone application, to try to offset the joining fee for Apple's Developer Program.
I'm currently beta-testing it. If you're interested, you'll need to log in with an OpenID, download and configure the the irssi script, and do one or both of the following:
The source code for most of the infrastructure for iIrssi is available in my git repository.