Now that the power struggle with Vivendi for control of PTC/Era is over (with a cash payment from Deutsche Telekom to Vivendi), Era is going to be rebranded T-Mobile:
The Warsaw Voice
However, in what is now pretty much standard proactice in rebranding, the "fake" MVNO Heyah will remain a separate brand, and the Era prepaid brand, Tak Tak, will be kept under T-Mobile. Before the URL switches on the 5th, T-Mobile.pl provides rebranding info:
Era zmieni się w T-Mobile