Actually – dialing the modem is now easier: with latest Gutsy Gibon, after you setup the connection as above, the network manager (the wireless/wired connection manager) will now offer the option to “connect ppp0 via modem” under “dial-up connections”. Clicking on this will dial the modem, and you don’t need the modem dialer anymore.

The same menu also offers the option to disconnect when you’re done with the network.