Will copy and paste my answer to this same question earlier today, to someone going to France and Spain for 90 days :
”Firstly, you need to change the APN in your phone / router to ‘mob.asm.net’ to access data abroad. There are two posts pinned at the top of the “chats and hacks” section of this forum, one for Android and iPhone, that tell you how to do this.
(FOR ROUTERS, read it’s manual, Google it or contact the support team at your router’s manufacturer)
You can use up to 12 GB of data when roaming abroad with Smarty, which can be eaten up pretty quickly if you use the data with Apple or Google Maps for navigation in Belgium and the Netherlands.
The problem which you may have is that Smarty can suspend all services on your account if you are abroad for more than 60 days.
It would be worthwhile you looking into travel eSIMs like Airalo, Holafly, Sparks, etc as long as you have an eSIM compatible phone. Videos about eSIMs are available on YouTube.
It would also be worthwhile looking at a French or Spanish SIM card (Belgian and Dutch SIM Cards in your case) which because of EU roaming rules, will work just as well in the other country, i.e. A French SIM or eSIM will work natively in Spain and vice versa. That applies for SIMs and eSIMs throughout the 27 member EU states, including Belgium and the Netherlands in your particular case)
https://help.smarty.co.uk/en/articles/2090500-roaming-and-international
