Can I also surf/call unlimited abroad?
You can. Up to 11 GB there are no additional costs for the EU. Your usage within Belgium isn't included in this 11 GB: only what you use outside of Belgium is. If you use more, every MB used in the EU will be charged at € 0,0053/MB. If you use over 20 GB during your bundle period, both within Belgium and abroad, you'll be able to continue surfing at a reduced speed of 512 kbps.
Outside the EU, the normal roaming rates apply, and you can’t use your Unlimited data bundle.