I believe there are several caching apps available for the iPhone/touch but am not sure how much/well they store cache info offline. If I had an iPhone, I don't think I would need as much offline data. But I only have an iPod touch and can't have too much data.
We cache with a VistaCX, two GPSMAP60csx GPSrs, and an iPod touch. We download pocket queries to GSAK (running on a Mac with Parallels) and upload filtered caches as waypoints (name, difficulty, terrain) and POIs (last 4 finds, hint) to the GPSrs. We then export the same information from GSAK as a custom HTML file. Then we use a program called GSAK2iPhone to make the HTML more iPhone/touch friendly. The HTML files are transferred to the iPod touch via another app called AirSharing. The cache pages (descriptions, images, logs) can be displayed as local web pages by AirSharing.
Seems like a lot of work but it only takes a few minutes. Nothing worse than being out in the field without some nugget of information that was in the cache description, on the page, or in a previous log.
Hope this is helpful.
D2M2