Do what EVERYONE does, purchase a cell phone each. As a non-resident, you can only purchase a "movil" which requires you to "recharge" your account, but that is very easy, every tobacco store, film place and department store, etc. sells little cards for 10, 15 and 20€. You call the number on the card, input the code number and bingo! your credit is updated. Besides, you never miss a call, and never have to use a pay phone, can call international long distance too. The mobile system here in Europe is much more advanced than it was in the US when I left in 2000. "Try it, you'll like it!" Besides, any new friends will automatically ask you for your "movil" number.
Telefonica is a huge ripoff, can take months to get installed, horrible service. If you want a DSL line, check out ya.com. Its a better deal. Also there are other phone companies competing with Telefonica, which is run by the government. I highly recommend staying away from Telefonica based on personal, awful, experience.