There is a Zenbu app for the iPhone available now, http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=289677153&mt=8.
With Version 1.0 you get full text search of 51,281 Zenbu listings from www.zenbu.co.nz (exported Aug 28) with full detail display and a handy list of other nearby listings, all without a network connection which is great for those of us not on a big data plan. All of this will take up less space on your phone than 2 songs.
The fact that it runs offline means you may not be getting the 'freshest' data, but most Zenbu content is pretty static so semi-regular application updates should mitigate this issue.
1.0 works on iPod touch or either iPhone. Version 2.0 will all look to utilise the location-awareness features of the newer iPhones.
It's free of course and I look forward to any feedback. Here or email@example.com
Chief Zenbu Bloke