In the process of EU integration, toward the EA accession, we try to understand, how changes in exchange rate regime, attributed to the switch through the ERM-II and to the EA accession, influence the dynamic between inflation and unemployment, i.e., shock on the Phillips curve coefficient. We look at a panel of countries, in the CEECs over the last twenty years, using a recent work from McLeay and Tenreyro (2020), to clarify the impact of loosing the monetary autonomy. Being under a pegged regime is not associated with a flattened Phillips curve. However, after the EA accession, the Phillips curve coefficient becomes not significant. This result is confirmed, looking at other small EA countries; while "economic leaders" tend to maintain a significant trade-off between inflation and unemployment. Using recent work from