I set up a internet system for a small camp site and I have some
customers who pay me each month for a connection to it. I also
installed some voip adaptors for them, so they could have a phone. At
the moment I just give them Sipgates details, they set up an account
with them, and I set up the voip adaptors with the sipgate details
they are given, from there on they deal with sipgate direct for paying
their account.

It looks like the camp site is going to expand, which got me thinking
that rather than just earn some money on the initial installation of
the voip equipment, perhaps I should be looking at earning some money
from the calls they make after the installation.

Question, how easy is it, and what is involved (in simple terms) to
achieve my aim?

Regards
Mark in Spain