The ESNcard is the membership card of the Erasmus Student Network.
With it, you get discounts all over Europe. If you wnt to check out all of them, go to the ESNcard website.
When you buy an ESNcard at the Buddynetwork TU Wien you also get a bag full of goodies which includes a SIM card (on request). The card costs 10€ and you can get it in our office during our Office Hours every Monday from 5:30 to 6:30 PM.