"I will have bought a cell phone."
Translation:Εγώ θα έχω αγοράσει ένα κινητό.
When translating in GR one can definitely skip the "εγώ" and the "ένα" as they would only be used for emphasis.
Also "cell phone (US) / mobile phone (GB)" is "κινητό τηλέφωνο" in GR and should be accepted as correct. Or one could just say "cell / mobile = κινητό" as all countries/languages mainly use the short term of the device's name in my experience :-)