Any prepaid (prepago) SIM from Vodafone in Spain can be used for internet access. Initially you are charged at 2 € per MB. There are better deals if you use more than a few MB:

Volume Tariffs

Basic: 20 € for 25 MB (or as Vodafone says 100 sessions)
Advanced: 40 € for 200 MB
Premium: 60 € for 1 GB
All these are valid for a maximum of three months. After that you are back on 2 € per MB automatically.
To get the deals you just have to send a SMS to number 2207 with either the following depending on which deal you want:
C BAS
C AVA
C PRE


Week, 2 Week and Month Tariffs

Looking at this page, there is also an option to surf for a week (29 euros), 15 days (39 euros) or a month (59 euros). After 1 GB, your speed drops to 128 kps. Activate by SMSing C SEM, C QUI, C MES, respectively, to 2207. Activation is instant, no waiting period.


Misc Info:

• APN: airtelnet.es
• Username: vodafone
• Password: vodafone
• Store Locator: http://www.vodafone.es/atencion-al-cliente/cerca/tiendas/ (Note: Lists all stores in which Vodafone equipment is sold. Not certain all of them sell stand alone prepaid SIMs. To be investigated)
• To check the balance: *134#
• When I bought the SIM card, it cost 24 euros with 30 euros already on the account. To see how much you need to top up in addition to the initial balance (which could change over time due to promotions etc), it is worthwhile to first check the balance with *134# and then decide on the additional top-up.
• Important: Remember your phone number, as you need it to top-up.