Confusingly the you need to install the package: imap-2002.
UW POP is not a service, it's one the programs handled by the xinetd service. To activate it, edit /etc/xinetd.d/ipop3s (ipop3 for non-SSL mail) changing:
disable = yes
disable = no
There's no other configuration required for mbox spools, don't know about maildir.
Then restart the xinetd service:
/sbin/service xinetd restart
To check that it's live, list the active ports on your box:
look for the pop entry.