Customs fees are usually luck of the draw. Don't think that you will get a fixed figure on that.
It should be fixed amount. Following the link http://www.sars.gov.za/Legal/Primary-Legislation/Pages/Schedules-to-the-Customs-and-Excise-Act.aspx you can find tariff book with fees for different type of imported goods. I've tried to receive assistance from customs support on this document - no success
That is why I would like to hear couple of factual cases with this particular phone - how much it is going to cost to bring the phone in the country.
Thanks.