Today, using my nifty osx-pl2303 driver for my Tripp-Lite U209-000-R USB-to-serial adapter and screen, I was able to get a serial console to a server in my office. Specifically, I typed:
screen /dev/cu.PL2303-0000101D 38400
When I was done, I typed: ^a^k to kill the terminal session. Since screen(1) is part of the base OS X install.