always best i find, to use wvdial and wvdialconf to get online first, if you can connect using that then you can think about using kppp or something else as annoying
i always thougth the sm56 wasn't properly supported, guess it must be if you get that far.
if you still get problems, it's worth setting up a log file for debugging ppp. you can specify one in /etc/syslog.conf, but i can't exactly remember what to put in it, as i'm not near my box now. there was a good document abouting setting up ppp that says how to debug it better, search somewhere for 'ppp setup', should find it.