I think it is important to post this information on this sub-forum as well
Roaming charges for use of an EU (+Norway, Iceland and Liechtenstein) phone subscription on any other country within the area will be abolished on June 15th 2017.
This means one single GSM card for your unblocked smartphone, with a decent amount of GB included on a prepaid plan, will be enough to cover your basic internet access needs throughout your trip, without the need to canvass open Wi-Fi networks.
Official source: http://europa.eu/youreurope/citizens/consumers/telecoms-internet/mobile-roaming-costs/index_en.htm