Just to add my experiences:

/dev/ttya receives fine, but sends garbage characters one-for-one
	corresponding to my keypresses
/dev/ttyb works great -- no problems transmit or receive
/dev/modem has GIGO as well as some actual AT commands and normal responses.

I also want to add a "me too" to the other posters thanking you for
getting serial ports working!

Do you think serial ports are working well enough to go on the
NetBSD/sparc News section?

  -- MW