Using sources from April 10, I've had a little play with the nell driver.
Taking a look at the i386 configuration file, I added :

## PCMCIA serial interfaces
com*	at pcmcia? function ?		# Modems and serial cards
pcmcom*	at pcmcia? function ?		# PCMCIA multi-port serial cards
com*	at pcmcom? slave ?		# ...and the slave devices

## PCMCIA SCSI controllers
aic*	at pcmcia? function ?		# Adaptec APA-1460 SCSI
esp*	at pcmcia? function ?		# Qlogic ESP406/FAS408 SCSI

## PCMCIA IDE controllers 
wdc*	at pcmcia? function ?           

## PCMCIA network interfaces
an*	at pcmcia? function ?		# Aironet PC4500/PC4800 (802.11)
awi*	at pcmcia? function ?		# BayStack 650/660 (802.11FH/DS)
cnw*	at pcmcia? function ?		# Xircom/Netwave AirSurfer
ep*	at pcmcia? function ?		# 3Com 3c589 and 3c562 Ethernet
mbe*	at pcmcia? function ?		# MB8696x based Ethernet
ne*	at pcmcia? function ?		# NE2000-compatible Ethernet 
ray*	at pcmcia? function ?		# Raytheon Raylink (802.11)
sm*	at pcmcia? function ?		# Megahertz Ethernet
# tr at pcmcia has problems with Cardbus bridges
#tr*	at pcmcia? function ?		# TROPIC based Token-Ring
wi*	at pcmcia? function ?		# Lucent WaveLan IEEE (802.11)
#xi*	at pcmcia? function ?		# Xircom CreditCard Ethernet

#mhzc*	at pcmcia? function ?		# Megahertz Ethernet/Modem combo cards
#com*	at mhzc?
#sm*	at mhzc?

## PCMCIA audio devices
#esl*	at pcmcia? function ?			# ESS 1688 AudioDrive

to my kernel config (the commented drivers didn't compile).  I have a 
Megahertz 33.6 modem that came with my Sparcbook, so I tried that.  Added
/dev/ttyC0 and inserted the card :

stp4020[0]: Battery change 2
stp4020[0]: Battery change 1
stp4020[0]: Battery change 1
stp4020[0]: Battery change 2
stp4020[0]: Battery change 2
com0 at pcmcia0 function 0: serial device
com0: ns16550a, working fifo

Connected to it with cu.  No response and I can't quit cu.  Hmm, eject card :

com0 detached

and cu exits.

Tried a few more times, third time, got a succession of attach/detach
messages.  Popped the card out, inserted it a fourth time.  Instant reboot,
no messages ;-(

J

PS.  With 1.5ZC (versus the 1.5ZA I had previously), my SS20 seems really
sluggish.  If I run one program that uses lots of CPU, I can watch the
screen repaint and xterms scroll line by line.

-- 
                    My other computer also runs NetBSD
                          http://www.netbsd.org/