Have you considered this:
Vodafone: Tarifa Plana Mini 24 horas
It gives 350mins a month of calls to Vodafone and unlimited calls to landlines for around 20 euros per month.
Generally speaking all the prepaid plans from the main network operators here (Movistar, Vodafone, Orange) are rather poor value for money. There are good options for people who make a lot of long calls, (like the 90x1 as mentioned) but if you make many short calls, these are often not very good, as the cost of the first minute is expensive.
Even for calling within network, you are often better getting one of the many prepaid plans from the discounters like Blau, Simyo, yoigo, Masmovil etc. The cheapest rates are 8c (exc. IVA). Just watch out for connection charge cost, and if there is a min monthly spend requirement.