The move is seen by the EU institutions as a major victory for the EU and part of a broader effort to create a digital single market.
"The end of roaming charges is a true European success story," said European Commission president Jean-Claude Juncker in a statement.
Big operators across the EU have agreed to comply with the new "roam like at home" rules, doing away with surprise prices and large bills.
But there are exceptions to the rule.
EU officials earlier this week told reporters that several dozen small virtual operators, out of thousands, had asked for derogations in order to maintain roaming charges.
"It is only virtual operators, who in general, have an extremely limited slice of the market," noted one official.
Those derogations are concentrated in Finland, Estonia, and Lithuania, where operators already offer cheap rates when compared to other EU states.
No requests for exemptions to the roaming-free rule were made in the big EU member states, such as Germany, France, and the UK.
Italian regulators are currently analysing exemption requests made by two small virtual operators.
The EU commission has also identified isolated cases where operators have increased their rates to offset roaming losses in Denmark, Latvia and Norway. But elsewhere, like in Greece, the price has actually decreased.
"We don't see an increase Europe-wide, but actually we see a trend towards a slight reduction," noted another EU official.
Operators have an option also to apply a so-called "fair use" policy that may impose caps on how much mobile data can be used while abroad.
The "roam like at home" principle only works if you spend more time at home than abroad.
But if operators detect, over a four month period, that you spend more time abroad than at home, they can impose a surcharge of up to a maximum of €7.7 per GB of data. In 2007, operators were charging up to €6 per MB.
Calls received in another EU state won't be charged.
The new rules apply to all 28 EU member states, along with Iceland, Liechtenstein, and Norway.