The first bottleneck lies between your phone and your Internet service provider. Your phone, a perfect instrument for whispered flirtations with your beloved, is less adequate as a carrier of digital data. If your local phone exchange is one of the old non-digital variety, modern science can't help you. Line noise and static will repeatedly slow your connection. You're best off buying a voodoo doll to hang around the modem.
Digital exchanges make life almost bearable.
And if your internet service provider offers alternative local numbers, try switching between them when the going gets rough. It might also be worth trying the Pretoria number from Jo'burg, for example. The dirty secret of Internet Service Providers is that its the international connection which costs them the most money, which means its the area they're most likely to skimp on. The lesson is that the best times to surf are the worst times. Office workers migrate en masse to the 'net after lunch when boredom sets in.