Dont think the portability will work the magic Airtel is looking for.
As an individual sample ten members Friends, family en Colleagus how many have taken note, mentioned porting to another network? for me none of the above

Hence Airtel is loosing more money than they intend to make in Advertisement, Bonus airtime and free portability. While safcom is bussy adding value i.e just did adeal of 50M with huawei for cheep affordable handsets.
my two cents
The problem with the world is that the intelligent people are full of doubts while the stupid ones are full of confidence