I've seen all the usual pppd troubles, but this one I can't fix. If I run wvdial as root, everything works OK, if I run it as normal user, I get a "Cannot open device /dev/tts/1: device or resource busy"-error.
I'm pretty sure it must be another permission thing, since root works OK, but I don't understand what permissions to change. pppd is suid (I know: it's an ugly fix), both /dev/ttyS1 and /dev/tts/1 are chmod a+rw and /dev/tts/1 is in /etc/ppp/options. What am I missing here?
I've been trying things for days, please stop me from giving up!

What group owns /dev/ttyS1 on Mandrake? You probably need add yourself to that group. Or you could run wvdial with sudo?

Thanks, adding myself to the proper group did the trick. I'm back online, just before turning mad!