From June 2017 no network will be able to charge European residents extra fees when they make calls, browse the web or send a text while visiting another EU nation.
The new rules will spell and end to the post-holiday trauma experienced by many phone users who find unexpectedly large mobile bills waiting for them on their return.
As an interim measure call, data and text charges will be capped from 30 April next year, limiting operators to a a surcharge of no more than €0.05 (3.5p) extra per minute for calls, €0.02 extra per SMS and €0.05 extra per megabyte of data used.
EU officials say the caps will make roaming within the EU 75% cheaper during the interim period.