Configure with ./configure -with-imap=/usr/src/imap or where ever you built thfe UWashington IMAP Toolkit. This directory will be searched for a source installation. If no source installation is found there, then a package installation of the IMAP c-client will be searched for in this directory. If one is not found, then configure will fail.
A second configure option is to not specify a directory (i.e. ./configure -with-imap). This will assume that you have the imap-2004g source installed in the .. directory relative to the Asterisk source. If you do not have this source, then configure will default to the "system" option defined in the next paragraph
A third option is ./configure -with-imap=system. This will assume that you have installed a dynamically linked version of the c-client library (most likely via a package provided by your distro). This will attempt to link agains -lc-client and will search for c-client headers in your include path starting with the imap directory, and upon failure, in the c-client directory.
When you run 'make menuselect', choose 'Voicemail Build Options' and the IMAP_STORAGE option should be available for selection.
After selecting the IMAP_STORAGE option, use the 'x' key to exit menuselect and save your changes, and the build/install Asterisk normally.
2009-01-06