Not strictly a Voip question, about call blocking

I know its not strictly a voip question, but maybe you can help.
We use someone elses apartment/roof to launch our internet connection
(via a radio bridge link) to our complex about 5Kms away. At the
moment in return for this favour, we give them free internet access.
The incoming Telefonica ADSL line comes with free incoming phone calls
and free outgoing national phone calls. I would like to give the
people in the apartment the use of this facilty, but dont want to just
connect up a phone, just in case they start making expensive calls to
mobiles etc, and we end up in dispute. Any recommendations on units we
can fit in the analogue phone line connection (after the ADSL Filter)
that can be programmed so that users can only dial numbers starting
with the number 9 for example.

Your advice would be appreciated.

Mark in Spain.

Anti-Spam wrote:
> I know its not strictly a voip question, but maybe you can help.

This was multi-posted on to the parent group.

> We use someone elses apartment/roof to launch our internet connection
> (via a radio bridge link) to our complex about 5Kms away. At the
> moment in return for this favour, we give them free internet access.
> The incoming Telefonica ADSL line comes with free incoming phone calls
> and free outgoing national phone calls. I would like to give the
> people in the apartment the use of this facilty, but dont want to just
> connect up a phone, just in case they start making expensive calls to
> mobiles etc, and we end up in dispute. Any recommendations on units we
> can fit in the analogue phone line connection (after the ADSL Filter)
> that can be programmed so that users can only dial numbers starting
> with the number 9 for example.
>
> Your advice would be appreciated.
>
> Mark in Spain.