Using the phone in Spain works pretty much the same as in any other country. Almost all foreign countries can be direct-dialled.
All national Spanish calls are billed in the same way. You pay an amount for establishing the call (around 15 cents) and are then charged per minute connected. All telecoms charges are subject to IVA (VAT).
Call charges vary depending on the destination and time of your call. Nearly all companies have normal and off-peak rates and most offer different calling plans for different levels and types of calling. As everywhere, it is quite complicated to work out what is the best deal, but it can be worth the investment of time. One thing to watch out for is that calls from fixed lines to mobile phones are expensive (around 20 cents/minute at standard rate).
Spain also has premium-rate numbers that start with special prefixes (900, 901, 902, etc.), which are generally used by companies for customer hotlines. This is a non-exhaustive list of these prefixes and what they mean:
International calls are expensive in Spain. Even if you use an alternative provider the charges can be heavy, so it is worth investigating the different plans on offer. The cheapest solution is to use an international prepaid calling card with your normal fixed phone and pay your provider just the cost of a local call.
If you want inbound phone calls redirected to another number (desvío de llamadas), you need to phone Telefónica to get them to enable the service. You will pay a small monthly charge and the cost of the forwarded calls.
To activate:
To deactivate: