[Resolved]  Nokia N73 — calling key not work

i am having nokia n73 music edition, i purchased my mobile in 27.12.08.
my mobile still in warranty period ..


problem is that when i open contact list & press calling button . the button is not working . but when i used speed dialing it works.. i gave my mobile to nokia customer care on 20.08.09, he tell that there is software problem, he flash up the mobile.. then it properly works 6 day, then it again not working on 26.08.09, i again go to nokia customer care on 27.08.09 now he says that there is key problem, he change the key, then it work for 5 hours, now it again not work properly. what am i do now?
can nokia change my mobile... plz tell