Unfortunately dial-up Internet connections are not fast enough for VoIP.
A reliable broadband Internet connection such as dsl or cable is what
is needed for high quality VoIP. The minimum bandwidth required for VoIP
is 88 kbps in both the upload and download directions. If you are
unsure if you have enough bandwidth for VoIP you can use a VoIP speed
tester to test your Internet connection. Business users who might want
to use multiple VoIP phone lines at once will require more bandwidth
than residential users. An easy way to calculate how much bandwidth a
business user might need is to multiple 90 kbps times the maximum number
of business VoIP telephone lines you will be using at any one time. So a
typical small office with 3 business VoIP telephone lines will need (3
times 88 kbps = 264 kbps) in both the upload and download directions. A
good rule of thumb is to limit VoIP usage to no more than 50% of your
maximum Internet bandwidth to be sure that you are always getting the
best quality signal.