As Redmine is Project tool for developers, managers and any other kind of persons and any kind of projects - like software,
sample design task, organizing events should be useful if Redmine site have Contact database with Customer, Client,
Partner, Employ contact information.

Contact information person can bet also attached for some projects, and people who is working with him necessary project
can find necessary person with whom contacting.

If it's necessary for every contact person you can relate with user name and this person can get access for some project.

If you need a support about AJAX & UI for this issue, don't hestite to contact me.