The
advertised international rates in the "Smartphone Fun S" tariff are all you pay and not a surcharge to domestic rates.
But be aware that Vodafone charges a connection fee of € 0.15 for each successful international call and since statistically most calls remain below 2 minutes, you practically pay more than those 5 cents. That's why calls to Polish landlines appear cheaper than they actually are. Also be aware that calls to mobile networks are significantly cheaper to countries which use the calling-party-pays regime (which includes nearly the whole world except for North America).