Using OR for Nesting Multiple IF

Hi guys, i have difficulties of getting the formula right for this following file here. what i am trying to do is to change the fields in Column A to another product.
The formula that i am using is : =OR(IF(A2="a1",Iphone,""),IF(A2="a2","samsung",""),IF(A2="a3","HTC",""),IF(A2="a4","Nokia",""))
I need a1 to change to Iphone, a2 to Samsung, a3 to HTC, and a4 to Nokia. attached file.