A data-only SIM card is a SIM card which can only be used to connect to the mobile data network. Only mobile Internet, that is. You won’t be able to make calls or text with a data-only SIM card. A data-only SIM card can be topped up for € 12, which will give you 2GB mobile data for a month of surfing the Belgian network carefree.
Please note: a data-only SIM card cannot be used abroad. It is not possible to combine it with a subscription.