To use smartphone as a modem, it is enough to switch of more advanced means of providing internet to a computer, like USB tethering.
Plugging Samsung Galaxy S plus into USB automatically brings up Kies application and, after the connection is established, the clever little thingy appears like /dev/ttyACM0 .
From here onwards, one can treat it as a modem.
A problem I encountered was that after a certain period (of inactivity?), the phone disappears from /dev . Removing module
cdc_acm and then loading it again allows one to use his favourite
dialing application to reconnect. My platform is Asus EEE PC 1015PEM/Debian Squeeze .