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Update: Someone on Hackernews argued that international charges would still apply. However, according to this [1]:
"International call charges would be capped at the price of a long-distance domestic call and intra-EU mobile calls at €0.19 per minute (plus VAT)."
there would be no difference between domestic and (EU-)international, eventually creating the coveted single market.
From Ryan Heath, spokesman of Neelie Kroes:
(Sven @1sveme)
@RyanHeathEU would the new roaming rule mean that a truly single market would be created? Could an Austrian company compete in Germany?
(Ryan Heath @RyanHeathEU)
@1sveme yes. You could buy your mobile subscription from another EU country and a company could easily set up in another country
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[1] http://ec.europa.eu/news/science/130916_en.htm
(update: edited for clarity, damn, I don't get those formatting possibilities on HN)
Roaming traditionally refers to using your phone outside of its network country. So calls to that phone will still be charged an international call charge.
Then again, if you have a data plan, coupled with some kind of VOIP service, you could effectively use your phone across all of Europe for the simple price of an unlimited data package.