Call Waiting will cause your connection to Spacelink to drop out if someone tries to ring while you are on the Internet. Use these numbers to toggle call waiting on and off. If you received, from Telstra, a Touch Phone 2000 when your phone line was installed and you have one connected to the same phone number somewhere else in the house, this could be causing the problem as well. The amount of current they draw is enough to disrupt your connection to Spacelink. Try unplugging all the other phones in the house before you dial in, in order to determine if they are causing your problem.
Faxes are a big culprit as well.
If you are connecting to Spacelink using your fax line, it is recommended that you remove your fax from the line also.