Where the installation of landlines are considered uneconomic by Telefónica, they may offer a radiophone. With this you can at least make phone calls, subject to Telefónica's tariffs.
If it's one of the old-type radio phones and you want internet access, forget it! At best you might get the speed of a GSM mobile phone, at worst, nothing!
If it's one of the new phones, the internet will certainly still be very slow and intermittent, and can't compare with broadband speed.