There are 3 big providers in Hungary: t-mobile.hu, telenor.hu and vodafone.hu. Their websites are working in English, too, so you could check them out before you actually get there. T-mobile and telenor definitely have pay-as-you or prepaid plans. I also know from experience that telenor's phone customer service also is available in English locally but I assume the other two have that, as well. If you want to use your Hungarian sim card anywhere else in Europe, you will pay for roaming but I don't know much about this piece to the picture. Enjoy your time in Budapest! It's a great place.