Europe roaming from June 2017- single market?

The suggestion you make was exactly why telecom operators objected to these regulations. A compromise has now been found that you cannot use this trick continuously.

Quoting from the 30 June 2015 press release Roaming charges and open Internet: questions and answers:

The rules prevent abusive uses: for example, if the customer buys a SIM card in another EU country where domestic prices are lower to use it at home; or if the customer permanently stays abroad with a domestic subscription of his home country. This is not the usual use of roaming as the vast majority of Europeans experience it. These unusual behaviours are also called ‘permanent roaming’ and could have a negative impact on domestic prices, and ultimately on consumers. This is why there is a fair use safeguard. Once that limit is reached while being abroad, a small basic fee can be charged. This will be much lower than current caps (maximum prices that operators can charge consumers for roaming in the EU) and is likely to decrease even further. The Commission has been mandated to define the details of the fair use limit.

From the 22 september 2016 press release Questions and answers on fair use policy and other preparatory measures it seems that an exact definition of fair use is left to the operators. The release talks about Rules on "fair use" measures that operators can take (emphasis mine). Some guidelines are given, however:

Fair use policies have to be notified by the roaming provider to the national regulatory authority.

• Fighting commercial abuses. Abuses could be related to the mass purchase and resale of SIM cards for permanent use outside the country of the operator issuing them. In such cases, the operator will be allowed to take immediate and proportionate measures while informing the national regulator (e.g. suspension of service on the basis of breach of contractual conditions). The operator has to simultaneously notify the national regulatory authority about the evidence of the systematic abuse and the measures taken. This enables the national regulatory authority to monitor the application of that measure in accordance with the established requirements and to react if necessary.

• Individual abuse by customers.Roaming is for travellers. The new draft allows operators to check usage patterns to avoid the abuse of the "Roam like at Home" mechanism. A non-exhaustive list of criteria includes: insignificant domestic traffic compared to roaming traffic; long inactivity of a given SIM card associated with use mostly, if not exclusively, while roaming; subscription and sequential use of multiple SIM cards by the same customer while roaming. In such cases, operators will have to alert their users. Only if these conditions are met, operators will be able to apply small surcharges (the Commission proposed a maximum of €0.04/min per call, €0.01/SMS and €0.0085/MB). In case of disagreement, complaints procedures must be put in place by the operator. If the dispute persists, the customer may complain to the national regulatory authority who will settle the case.

Creating a single market for telephony in the way you describe has never been the goal of these regulations. The basis for the discussion has always been that roaming was for travellers and customers would continue to get a mobile phone contract locally and operators have been fighting hard to keep it that way (see, e.g., this press release issued by the Commission last September).

The regulation should therefore merely make incidental use in another EU country easier. Concretely, I remember talks of limiting free roaming to a certain number of days in a given year and the Commission now seems intent on letting operators and national authorities determine what’s incidental or not but nothing is final yet.

Importantly, roaming is free for customers but operators still have to pay to use another operator’s network. This “wholesale” price is also capped, but (obviously) not planned to go all the way to 0. This means that in your scenario, the Romanian operator would have to pay quite a bit to the Swedish operator, possibly eating up all their profit. The restrictions I mentioned before are intended to allow them to terminate your contract if they can determine that roaming charges are disproportionately high and Romania is not the primary place of use (not that it will not necessarily be about any specific legal notion of “residence”, the press releases uses the phrase “stable links” instead).

Unfortunately, this also means that getting a SIM card for long-term travel or keeping it alive from abroad could be more difficult than it is now, when operators can charge you for roaming and have fewer reasons to prevent customers from roaming a lot.