I hope this helps:
International Roaming will be enabled by default on all Afrihost-Purchased SIM Cards.
Activation and De-Activation of the service can be managed by calling the MTN Call Centre on 808.
Existing Data and SMS Bundles do not apply internationally and all transactions will be deducted from your Airtime Balance.
The rates will be the exact same as specified on the MTN Roaming Page at https://www.mtn.co.za/everyday_services/RoamingInternational/Pages/UsingPhonesAbroad.aspx
You will also need to ensure that your APN (Access Point) is set to the default and not "Afrihost" when roaming.