It means the prospects for a landline-based company are so bad that its real function is to morph into something that it is not.
This is exactly the kind of bizarre "mobile mentality" that seems to have beset much of the thinking about telecoms in developing countries, and apparently actively encouraged by amateur commentators and some analysts.
Mobile has certainly grown rapidly to deliver services to people (as opposed to places, like offices and houses), and has become a de facto substitute for poor fixed line services in many developing countries (South Africa included). However, this does not mean that mobile is all there is to telecoms, and it certainly doesn't mean that mobile is the answer to future broadband (and especially FTTx) demand, or to the rest of the revenue-generating telecoms space, dominated by corporate communications, not individuals.
In most developed countries, the need for broadband, fixed (place) communications is recognised alongside mobile. There is not often confusion between the two, and there is a narrow overlap, where substitution takes place. Analysts looking at operators in these countries certainly support the idea that a balanced operator looking to the future should have exposure to both mobile and fixed, to take advantage of the best of both, but that's not the same as assuming that fixed is dead.
To take the example at hand, Telkom would be a much more profitable company if it only provided corporate fixed line services, and didn't have to deal with a large base of consumers. Its revenues would be somewhat lower than they currently are, but its data growth prospects would probably be higher. There's no question of improving this by morphing into a mobile company. Just exactly how do you substitute a national STM-1 leased line by a cell phone. Does Lesley Stones even know what an STM-1 is?