I am writing this question in the train from Roosendaal to Leiden. The train provides a decent wireless internet connection. I have seen it before, but then it was an experiment on trains between Rotterdam and Utrecht with very wonky connections. Are the wireless connections now common on all trains and if not how can you know which train has wireless internet?
From the website of the largest traincompany, NS
Draadloos internet in de trein
NS en haar partners bieden u gratis draadloos internet in de trein aan. Draadloos internet is nu nog in een beperkt aantal Intercity's beschikbaar, maar dat worden er steeds meer
- U herkent een Intercity voorzien van draadloos internet aan het Wi-Fi logo aan de buitenzijde van de trein
- Hoe werkt het? Reist u met een trein voorzien van draadloos internet, ga dan op uw laptop of telefoon naar 'Verbindingen'. Daarna kiest u voor 'Wifi in de trein'
- U kunt daarna direct online om te internetten, chatten en e-mailen
- Draadloos internet in de trein is gratis
Basically, you will find free (!) Wifi in certain Intercities (the quick trains between different cities) only. These trains are not specified on beforehand, but you can recognize these trains from the Wifi-logo on the outside of the train. You have to connect with the "Wifi in de trein"-network.
For now, the usage of the Wifi is free, but if I remember correctly they are mainly performing tests at the moment, so certainly not all trains are equipped with the free Wifi.
I expect it to become a paid service when it is fully operational on all trains, but I do not have a source for that.
To add to the answer and comments above, yes there is wifi in some trains and yes it's free. Sadly also, yes, it's slow.
There is no way to determine what train will have wifi when planning your route, it won't even be certain that if you take a train that leaves every day at let's say 10.00 it will have wifi every day because trains get switched up a lot.
I actually called NS about this because I had a long train ride ahead and needed to do some work, they can't promise or guarantee anything. So all I can tell you is: There is a slight chance you will have free, slow wifi.