"I'M GOING TO BE HAVING RENTERS IN YHR HOUSE I OWN. HOW DO I SAVE MYSELF FROM HUGE INTERNATIONAL BILLS?"
The OWNER of the phone line (the name on the bill) - ONLY - must go into an ICE (the local phone monopoly) office (anywhere) - along with their ORIGINAL cedula or Passport to request and ask:
"Quiero bloquear las llamadas internacionales de mi lÃnea telefonica".
If the line is in the name of a CORPORATION / S.A. - you also need a NEW (within less than 30 days) "Personera Juridica" from a lawyer (the times I've had to get a new one it ran 10,000-colones/$20 (more if it was a rush).
FYI - in my last home - we could NOT make ANY changes because the phone line was in the name of the original builder of the house who was long dead as his name was still on it an the only way to make changes was for my landlord to go to court ICE said (though I'm sure some good contacts on the "inside" could have taken care of that!!!).
NOTE: If you have your landline blocked from making international calls, MY experience with 4 lines in 6-1/2 years has been that you also can NOT RECEIVE international calls as well (& the message your friends/family will get will be in Spanish - not great if they don't speak the ling).