It's a scam.
OK - not legally, I suppose, but in the sense that much of what Telkom describes as "value added" is just another money-making racket masquerading as a saving.
Yes, you don't pay for the faxes you receive, but someone else does, at ludicrously high rates - Rands, not cents, per minute. The money made from these calls goes into the pockets of the reseller you're getting the number from, from their wholesale provider (guys with a big, money-printing contract with Telkom), and, yes, you guessed it, Telkom. I'm sure they'll all tell you that they have to make a living, but they're not actually adding any value (other than a relatively inexpensive fax-to-email server that anyone can buy).
So who loses? Everyone I guess, since everyone's telephone bills go up as a result. All you are doing by co-operating with this scam is milking your customers, suppliers, or whoever you do business with. Your choice, I guess. If you don't care about anyone else's bill, and only your own, then my advice would be get a number yourself, but refuse ever to send faxes to someone else's 086 fax-to-email number. I just tell them that I don't support scams, and they can provide a normal fax number or an e-mail address. I hope I never have to send you a fax.
What we really need in this country is non-premium-rated fax to e-mail, using normal numbers.