so, a little bit late but maybe will be useful for someone else.
you can try wvdial, it is a great tool for connecting via dial-up and it is pretty easy to configure.
HERE'S WHAT I FOUND IN UBUNTU DOCUMENTATION:
Alternative Way 1 (using wvdialconf & wvdial)
I prefer wvdial, because it tells you whether your modem is configured or not.
It dials a modem and starts pppd in order to connect to the Internet. The connection started with wvdial can be dropped by switching back to the terminal from where it was started and pressing ctrl-C.
Type in a terminal
$ sudo wvdialconf /etc/wvdial.conf
If it says 'no modem found' or something similar, sorry... the driver for your modem seems not to be installed properly yet. Alternatively, you can try setserial. The lack of a /dev/modem is not supposed to break wvdial's configuration.
If the modem is found, finish the setup with:
$ sudo nano /etc/wvdial.conf
After opening the wvdial.conf file, input your ISP information where needed (look inside the file for fields) and add other options that might be needed for your software modem. You will know what these options are if you asked for help from linmodems.org mailing list. Examples options that you can try to add, if dialling does not work:
add X3 to Init2 (means dial without waiting)
add Carrier Check = no as a new line (useful for Smartlink modems)
add Stupid mode = on as a new line (will start pppd immediately--required by some ISPs)
Typing man wvdial.conf in a separate terminal will give details on options.
Once you are ready, save the file (Ctrl-o) and exit (Ctrl-x), and try to dial:
will dial and connect. If you are using the Ubuntu Live CD, you cannot save the file wvdial.conf
Upon connection, it will spit out some information about your connection (local IP, remote IP, DNS address, etc.). Do not close the terminal where wvdial is running. Leave it alone until you want the connection to be terminated, and hit CTRL+C on that terminal once you want to end the connection.
If you lose the connection a short time after connecting (30 sec - 3 min), you might need to edit options for pppd:
gksudo gedit /etc/ppp/options
Find lcp-echo-interval30 and lcp-echo-failure4. Comment out these options by adding a '#' at the start of these lines, eg. # lcp-echo-interval30 and # lcp-echo-failure4.
If you connect successfully but your Internet applications do not function (eg. web pages do not load in Firefox), you might need to add replacedefaultroute as a new line in the pppd option file.