I bought an Orange Dongle from Cartegena (can also get from Mazzaron where English girl works).
Dongle is about €50 and €4 per day - first 250mb is it top speed and then slows down after that.
Signal is fine on La Isla.
Have also bought a 3G router in UK and am taking that over this week so that the flat can have WiFi (kids can use PS3, I-Touches etc...)