The attached patch (relative to yesterday's state of the orgmode git 
repository) adds the possibility to have org-mode links to IMAP folders in 
VM and to messages inside IMAP folders. It requires VM 8.2.0a or later.

IMAP links have the format

	vm-imap:account:imap-folder-name

for a folder and

	vm-imap:account:imap-folder-name#message-id

for a message. The account:imap-folder notation is the same that is used in 
VM when entering a folder name in the minibuffer.

I ended up creating a new link type (vm-imap) instead of overloading the vm 
link type with some cryptic syntax. This also seems more consistent with 
how VM considers IMAP folders to be in a separate universe from local 
folders.

I hope this will be useful to others!

Konrad.