May be problem with configuration, but it was not working very well.

I tried both KNetworkManager and wvdial. I would say there were slightly more problems with wvdial.

Problems: Sometimes modem hanged up. I should better say it was wvdial who hanged up, as modem sometimes indicated it is connected by blue light on. Restarting wvdial was not enough, but restarting modem usually helped, sometimes it was necessary to restart 2 or 3 times. (It has never happened under WinXP, but I was using it most of the time under GNU/Linux, so it might be a chance.)