Reference???That agreement between Cell C and Vodacom didn't exist when I was a Cell C subscriber. Even if it did, who's to say Cell C wouldn't believe their worse than useless coverage is enough to not warrant costly Vodacom roaming? Something tells me Cell C isn't keen to use Vodacom in urban areas if at all possible.
Besides, you talk about the past when Cell C network was sabotaged by Vodacom towers. Listen feedback from the poeple who currently use Cell C, you will change your mind.