I think you may have misread the information, the price you're quoting is for the line rental alone. 4Mbps Uncapped data would be an additional R397 per month. However, if you bundle these together, you can save by paying a single amount of R597 per month.
This excludes your monthly service fee from Telkom for your voice line and any calls made from the landline. It is only for the DSL rental portion. It also excludes any installation fees levied by Telkom for line installation and DSL conversion. However, if you convert your line to DSL via us there should be no fee. You can also opt for a voice plan that comes with free installation to avoid paying either of these fees, which can come to around R1,500 once off to Telkom.