Can a user be in more than one department?

Yes. A person can belong to any number of departments, groups and roles on a production, so someone who's both a designer and a stage manager can carry both.

You'll need the Manage Groups permission on that production. Production Roles appears only if you also have Assign Users to Production on a production, or Add/Edit Productions and Assign Users, and opening someone else's profile takes Edit Users on their production or Edit Any User & Private User Info.

1. Go to Administration > User Administration, click the cog on the person's row and choose Edit.
2. Click Production Roles in the list on the left.
3. Click Manage Groups beside the production.
4. On the Departments tab, check every department they belong to. The Groups and Roles tabs work the same way.
5. Click Next. The next window lists what they're being added to and removed from, and the date the change applies to calls from.
6. Click Save.

Being in two departments means they get the calls, discussions and files sent to either one.