LONDON, 2015-5-12 — /EPR Retail News/ — From 6th May – 30th September 2015, Mobile by Sainsbury’s, [the MVNO] launched in July 2013, is slashing the cost of roaming in over 30 European countries, including top holiday destinations such as Spain, France and Greece. Customers on Pay-as-you-go and SIM-only deals (launched 6th May) will now pay…