Sorry for my late reply. Belgium has three mobile networks: Base, Proximus and Mobistar. These three operators have normal subscriptions (postpaid) and pay as you go plans, but are pretty expensive with international calls / texts. When you make a lot of calls to Denmark or send a lot of textmessages to Denmark, the best option is to choose for a so-called Mobile Virtual Network Operator focused on international calls. You can search for an Ortel Mobile subscription (
www.ortelmobile.be). I think that's one of the most affordable MVNOs.
Have a nice stay in Belgium! When you have further questions, don't hesitate to contact us!
With kind regards,
Tim Wijkman