If your modem is connecting check Firefox (under 'File' tab) to see
that is NOT set in the 'work off line' mode. For some reason this is
the default setting for Firefox after you install Hardy Heron.

Ubuntu has (to my knowledge) not corrected the network connection
problem that started with 7.04, (they don't seem concerned with
dial-up any more), and continues with Hardy Heron 8.04. The network
connection icon will not show a connection even though you have one. So,
the modem will
dial upon boot-up and you are right, the easy way to disconnect is to
turn the modem off.

If your modem is not connecting, recheck your set-up under Network. Make
sure your password and isp user name are correct. Also check that
'modem' details are correct. If you always could connect under 6.06,
then you WILL be able to connect with 8.04. Keep trying!