The availability of a a good mobile phone signal DOES NOT mean you will have a good signal with a dongle!!! It is very very important to understand this.
In Portugal, and most of Europe, most operators still operate 2G/UMTS mobile networks which only transmit data (i.e. Internet) at a slow speed.
Broadband over the mobile phone network (such as in Portugal, Vodafone/TMN/Optimus Dongles), only operates at full broadband speeds when one in in range of a 3G equipped mobile phone mast. 3G is more powerful but its range and strength is much less than 2G. Furthermore, in some cases, one can receive a 3G signal outside a property, but if the walls are thick, one may find that you can only get a 2G inside a house. I have had several clients who have had this experience. They have bought a dongle and then find it does not work at the speeds intended inside the house. They then have to trail back to the shop and get their money back.
It is, therefore, imperative to test that you can receive a good 3G mobile signal in your property before purchasing the gear.