Nasti-
For phone calls to movil phones- use a movil! When you call from a reg. telf. it gets expensive. So use your reg phone for regular calls only. Use a phone card with your reg. phone for your international calls- that should keep your bills down.

As per avg. phone bills... hard to say- depends on who you're calling and how long you tend to speak on the phone. Avg from 40 - 60 euros. But it also depends on what services you chose with telefonica.

Here's info on phone what a phone call costs from your home phone to another fijo:
Nacionales
Tipo de Llamada Tarifa llamada mínima Tarifa Normal-Importe/minuto adicional (1) Tarifa Reducida-Importe/minuto adicional (1) FRANQUICIA (Número de segundos sin coste adicional al iniciar)
Metropolitana Connection fee: 0,0685 € reg hour additional minute: 0,0240 minute cost at reduced fare: € 0,0099 additional free seconds after additional connection(so if you don't talk more than 160 sec. you only get charged the cost of the connection of the call): € 160 sg.
Provincial Connecion fee: 0,0833 Reg. price add min: € 0,0384 Reduced fare: € 0,0264 Free seconds before charge:€ 0 sg.
Interprovincial Connection fee:0,0833 € Regular min: 0,0678 Reduced min:€ 0,0378 Free time after connection of call:€ 0 sg.

For more information go to telefonicaonline.com it should pretty much answer all of your questions. It gives info as per times for reduced fares/reg fares and costs from a reg phone to a movil and even breaks down how much calling different movil carries would be (Amena is the most costly, vodaphone, moviline and movistar are the same.