Yes, we have a landline too, and so I usually only use it to phone home when I've forgotten what I'm shopping for, or when I'm out walking. You can read about it and apply for it here.
http://www.masmovil.es/index-eng I'm not sure about the 6 month rule, since I use every month but that seems to affect most providers. I applied at a desk in IKEA, before I saw the web site. I chose automatic payments, so they just take it by direct debit monthly- having first alerted me by e mail. You can see or download a record of all your calls and costs.