IPhone and iPod touch
From Organic Design wiki
iPhone and the Vodafone network
You can get iPhones for around $900 in NZ (eg here), but I'm not sure if they work on the Vodafone of the shelf - you may need to get them unlocked and simmed from Kiwi iPhone.
Installing MediaWiki
There seems to be no problem installing PHP5 and Apache, but I don't think anyone has been able to successfully get MySQL running on it which means we wouldn't be able to run local MediaWiki instances on it which is one of the major uses I'd have for them. If we could run our wikia setup locally from the ipod, then we could carry on with development and collaboration without a net connection.
Some useful links to find out more about iPhone hacking.