Hi emily,
Unfortunately, most of the phone numbers listed on the electronic version of
SegundaMano.es are 906. Those are peak rate phone numbers.
Most of the classified ads in that paper are free so they make their money from the people who buy it. However, if you use the online version you are not buying it and thus they came up with another way to get money. A calling system through that number. I'm guessing it won't work outside Spain and I'd try it either. It could be very expensive.