[vageli]

You need passport or local id for prepaid purchase, at least in the EU countries to which I've been.

[the_mitsuhiko]

Czechia, Sweden, Finland, Ireland. There are more but plenty to pick from without registration and good prices.

[ficklepickle]

I just bought a vodafone sim in the UK without ID. It is supposed to work all over Europe, but I only tried the Netherlands.