OK, I'm going to indulge you even if you are being an obtusence.
It is an ad, because countless people will wonder what the message on their screens is about and they will tie it into your advertising. They will therefore want to get it (which is what ads are for). They will find they cannot and the advertising laws forbid ads for products that are not available. Heck, if that doesn't fit they'll make a new one to keep up with technology. Why you're
broadcasting to contract accounts is beyond me. The cynical amongst us will agree that it will boost calls during that time by those hypothetical average consumers that believe a discount will apply. I'm sure Vodacom has discussed the merits of it long ago despite the naive impression we're getting that they have not.
Oh and while I'm about it - there's also a rule about when you can advertise "up to x%". It can't be on a blue moon like your internet speeds

rolleyes