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There is only one camera roll on the iPhone. You can manage folders of pictures by the way you sync in iTunes, but not on the device.

There might be third party applications that help, but I've never looked for one.
 
actually I seen an app in cydia today that will give you the option of adding another camera roll.

I don't remember the name of it...i think it might have been in "sections" under "multimedia"

Regardless it's somewhere in Cydia...hope this helps a little bit.
 
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