Better check with your provider. With my contract texts also cost extra abroad. But as I said, a handful of texts or short calls are usually no big deal, just don't do lengthy calls without checking your rates.
My worst odysee in Wacken was one year when we arrived late on Thursday, put our tents up as quickly as possible, grapped a bottle of Jägermeister and rushed to the stage. None of us bothered remembering our location, plus we got separated later on anyway. It took me a good 4h cluelessly wandering across mostly pitch black camping fields before I found my tent, half of it in the rain. Fortunately I met many nice people on the way, one of them gave me an empty garbage bag that I could work into an improvised rain coat.
Two lessons I learned that night: 1) Being irresponsible at festivals is great, but with a minimum of preparation. And remembering the way to your tent is part of that, and 2) arriving in Wacken on Monday already is not only much more relaxing, but prevents doing too much stupid stuff at once. Two rules I live by every since...