with your codes in col a sheet 1 starting in A2 and your table codes/states in sheet 2 codes in A states in B
(assuming a1/b1 contain headers such as area code/ state on both sheets)
in sheet 1 cell B2
put
=VLOOKUP(A2,SHEET2!$A$2:$B$1000,2,FALSE)
(Where $B$1000= last cell in your range on sheet 2 ,change it if it isnt)
drag down formula to end of list on sheeet 1