ReckITT: I think i can do it? well it sounds like i can...haha.
What's the difference between 'Naked' and 'Clothed' plans? 'Clothed' plans assume that you have an existing POTS (Plain Old Telephone Service) line rental at your house, from a Telco provider such as Spark, Telstraclear etc... These clothed plans are our broadband service running over your existing phone line. They're cheaper because your line provider is already paying the line rental fees to Chorus. Naked plans are for people who aren't paying a provider for an existing POTS line at their home, in which case we have to pay Chorus for the copper line rental to get your broadband connected (hence the extra cost).
This is only if there is not already an xDSL service running down that existing line. It is not possible to have two different xDSL connections with different providers on a single line.
The service you're referring to in SA (Which sounds like a really odd way to sell a service) appears more like two separate logins/bandwidth pools/PPPoE sessions for a single provisioned xDSL connection rather than two physically separate connections. Exactly how this is done would depend on how the wholesale market works there. I would be interested to see how it is pitched to consumers on SA ISPs' sites if you have any examples of this.
You would not be paying twice for the same thing here, as two separate xDSL connections = two separate wholesale charges plus connection charges, plus no sharing of line speed, and different ISPs can offer different routing and value-adds (e.g. bundle discounts, support, freebies, et cetera).