Does anyone know if there is a prepaid sim card that can be used in multiple countries? I would be picking it up in Germany, but would also need it in Holland and Belgium.
Most of the EU SIM cards now work in multiple countries thanks to the EU's relatively new "roam like at home" rule. If the SIM card plan allows roaming at all, it will be at the same cost as in the original country.
Here's a recent thread about German SIM cards:
https://community.ricksteves.com/travel-forum/germany/update-for-obtaining-sim-cards-in-germany-2018
You may need to provide a German address to buy one.
Here's some more info on German SIMs:
http://prepaid-data-sim-card.wikia.com/wiki/Germany
You could also buy a SIM from the Netherlands, the UK or another EU country that doesn't require being in country to register/activate the card. I've been using a Dutch Vodafone SIM I bought on eBay for two trips now (and haven't used it in the Netherlands yet!) See my write-up on it in the technology-tips forum.
Occasionally people have an issue with a SIM card so might benefit from buying one from a mobile store in country, so you can have the agent there sort out any issues you might have.
Thank you Andrew. That's a lot of great information.