What is MAS?

MAS is a family of mobile plans, and each one carries a fair use policy that limits EU roaming. MasMovil caps roaming by reasonable use, working the cap out from your monthly fee and the price of a maximum gigabyte, so a plan can advertise a large allowance and still deliver far less outside Spain. The policy also notes that persistent roaming use can add charges. The practical point is short: the gigabytes on the tariff are not the gigabytes you use abroad. Read the fair use terms for your specific plan before you rely on the allowance while travelling.