Changing part of cells values in Excel

In Egypt all mobile operators will change their code adding a number as follows:
012 XXX xxxx ---> 0122 XXX xxxx
017 XXX xxxx ---> 0127 XXX xxxx
018 XXX xxxx ---> 0128 XXX xxxx
0150 XXX xxxx ---> 0120 XXX xxxx

010 XXX xxxx ---> 0100 XXX xxxx
016 XXX xxxx ---> 0106 XXX xxxx
019 XXX xxxx ---> 0109 XXX xxxx
0151 XXX xxxx ---> 0101 XXX xxxx

011 XXX xxxx ---> 0111 XXX xxxx
014 XXX xxxx ---> 0114 XXX xxxx
0152 XXX xxxx ---> 0112 XXX xxxx

I am working on a way to modify our address book, so I exported it to Excel.
Now I need a formula (preferred), or a script that would make this change to the whole sheet.
Your help is appreciated...