Trouble with a modem

[mau at alice.CSELT.STET.IT]

I bought a Best 2400EC modem (Taiwanese stuff, with MNP5 available) to
connect it to a Sun 4/330 using SunOS 4.1, but I did not manage to get it
work. It is true I understand nothing of hardware (I am a mathematician)
but I thought that it was not very much difficult than connecting a
terminal.  I created /dev/cua0 (maj 12, min 128) parallel to /dev/ttya,
changed /etc/ttytab and /etc/gettytab according to the System
Administration Manual, and called /etc/ttysoftcar -a (my prom revision is
3.0, anyway I even tried recompiling kernel with 0x0 flags) which returned
error. If I try to tip a telephone number, it turns out that "all devices
are busy".  Any suggestion?

                BITNET: LAFTESI1 at ITOPOLI
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                fake Internet: mau at alice.cselt.stet.it