Samsung SGH-D900 / Black Carbon

I have bought this phone less than a month ago. since the second day, and for reasons i ignore, buttons 1, 2, 4, 7 and * become unclickable every now and then and then after a while they recover and are clickable again... this is a big problem i am facing and would appreciate if anyone has faced such a problem to tell me whether there is a solution to it...