The Nokia Lumia 710 on T-Mobile was launched (and available initially) for $49.99 with a new two-year agreement, but certain retailers managed to give the phone away for free, given you agree to the contract.
However, the Lumia 710 is now listed online at T-Mobile for $39.99 which is ten dollars less than what we’ve seen officially from the carrier. There are no details regarding a certain period of time in which this offer is valid so it’s kind of safe to assume that the price will remain $39.99 (online). Additionally, if you switch to T-Mobile or add a new line, the carrier will throw in free accessories with value of $50 when you purchase a Nokia Lumia. These include black Nokia Lumia gel skin, car charger and/or Motorola Bluetooth headset.