Although a maybe similar problem was discussed recently i found no
solution.
On a Mac P475 running NetBSD 1.4 i get with ppp the following: 

Jul 30 12:04:56 zette chat[222]: ATDT0191011^M^M
Jul 30 12:04:56 zette chat[222]: CONNECT
Jul 30 12:04:56 zette chat[222]:  -- got it
Jul 30 12:04:56 zette pppd[220]: Serial connection established.
Jul 30 12:04:57 zette pppd[220]: Using interface ppp0
Jul 30 12:04:57 zette pppd[220]: Connect: ppp0 <--> /dev/tty01
Jul 30 12:04:57 zette pppd[220]: Serial line is looped back.
Jul 30 12:04:57 zette pppd[220]: Connection terminated.
Jul 30 12:04:57 zette pppd[220]: Serial link disconnected.
Jul 30 12:04:59 zette pppd[220]: Exit.

the script used is from: "http://www2.giganet.net/~mark/NetBSD/ppp.html"
with option for pap. 

ppp-up:
#!/bin/sh

/usr/sbin/pppd /dev/tty01 57600 connect '/usr/sbin/chat -v "" ATZ OK ATF0
OK ATDT0191011 CONNECT' \
crtscts defaultroute noipdefault modem remotename * user
0002119694863200685494000001

options:
asyncmap 0
passive
crtscts
defaultroute
lock
noauth
lcp-echo-interval 30
lcp-echo-failure 10
netmask 255.255.255.0
domain btx.dtag.de
mtu 1500
name 0002119694863200685494000001
disconnect /etc/ppp/ppp-down
debug

pap-secrets:
0002119694863200685494000001 * passwd

the ISP says, PAP is necessary.
bad networking conf?
thanks
michael