From the RTFM department, GNU Screen can be used like tip or cu. The manual reads:

Screen has built in some functionality of “cu” and “telnet”.

and

If a tty (character special device) name (e.g. “/dev/ttya”) is specified as the first parameter, then the window is directly connected to this device.

So doing the following on my FreeBSD desktop

screen /dev/cuaa0

neatly connects to the first serial port with a usable terminal emulator. Which came in handy today when one of my hosts panicked.