From the EC article:
Roam Like at Home rules enter into force on 15 June 2017. People will pay domestic prices, irrespective of where they are travelling in the EU for phone-calls, SMS and mobile internet. Read the background and step-by-step details on how the EU achieved the end of roaming charges. The gradual reduction of charges since 2006 results in the end of roaming charges in 2017.
Roam Like at Home in a nutshell
Phone calls, SMS and going online with your mobile device from another EU country will be covered in the national bundle. The minutes of calls, SMS and megabytes of data that a person consumes abroad within the EU will be charged the same as at home. People will not have bill shocks anymore.
If a person has unlimited calls and SMS, he/she will get unlimited calls and SMS when roaming in the EU. However if a person has unlimited mobile data or very cheap mobile data at home, his operator may apply a safeguard (fair use) limit on data use while roaming. If so, the operator will have to inform the customer in advance about such a limit and alert them when they reach this limit.
The EU rules ensure that such a roaming data limit should cover the normal usage patterns of most travellers. If a person reaches the limit, he/she can continue to use data roaming for a very small fee: up to 7.7€/GB + VAT, which is 6.5 times less than before 15 June 2017 and 25 times less than before that.
As long as a person periodically travels and spends more time in his home country than abroad over any 4-month period, they will fully benefit from Roam Like at Home. If a person gets charged extra, he/she should first contest those charges with their operator, who should have a complaints procedure in place. If the operator persists, the person should refer to the national telecoms regulator, who will settle the case.
If a person stays in another country within the EU longer than in his home country over a few months, the operator may contact him and ask to pay more. More information can be found in the Frequently Asked Questions (FAQ). A very small number of operators in the EU have been allowed by the national telecoms regulator to continue applying a small roaming surcharge after 15 June, in order to avoid negative effects on very low domestic prices. Such surcharges will be significantly lower than the ones applied before 15 June 2017.
There are some caveats above, sure, so do triple check with your operator before you travel. But mainstream operators in EFIGS will already have complied.
Now, all that's need is to make sure that you're in a EU country. And if you are, make sure that some idiots in charge of your country haven't started to take your country out of the EU, because when that happens you'll be utterly scuppered!