Have a look at Palringo from the app store.
Its free asnd it does the job of a Multi channel IM software.
Googl;e Talk, ICQ, MSN,Yahoo and some other one Ive never heard off.
Anyway within Palringo you can have /join Groups.
There is a big group called Iphone and a NZ group called NZIphone.
Jason from there is behind a new Iphone Portal called http://iphone.techzone.co.nz which is only viewable on your Iphone