T-Mobile and Vodafone both offer BIS (Blackberry Internet Service), but you need a special Blackberry SIM, which costs € 20 with both operators. T-Mobile seem to be better value as they give free BIS for 6 months (limited to 1GB), while Vodafone charges € 12.50/month for the "Prepaid Blox voor BlackBerry" tariff.
details at:
T-Mobile.nl: BlackBerry Sim Only
BlackBerry -Prepaid aanbiedingen - Mobiel Bellen - Persoonlijk
But you should be aware that once a Blackberry is registered for BIS with a certain operator you can not activate BIS with another operator. So if you have activated BIS with your operator at home, you won't be able to use any internet-based service even when swapping SIM cards.
We discussed this issue in detail
here.