Micro Sim Cards for Unlocked Iphone 4

I have a pretty good understanding of the availability of mobile phones/packages, etc, etc in Europe but was wondering....for those of you who've been over, and taken an unlocked Iphone 4, (which uses a micro sim card about half the size of regular sim cards), are micro sim cards fairly readily available over there?
I use the Iphone when travelling, but just put it in "Airplane" mode ...great ( my personal perspective) for music, maps, movies, internet(wifi), books, games, various apps, etc, etc, etc. However, if I knew that I could get relatively cheap micro sim cards, I may be inclined to use the phone as well. Any experiences?.....