Please be more specific.
Correct, it should behave in that way. How it works? When your SIM is registered to the home network, accounting on the back end knows you use home network. When you are roaming, your packets are tunneled to your home network and the same accounting system is involved in allowing you access and counting your data.Then, when you are on the telkom network, it should deplete the cheaper on network bundle first. When you roam obviously it should deplete the handle that includes roaming or if depleted your access would be knocked.
I wonder however if this is how it works?
It might also switch to the first one to expire when on the home network.
When I check *180# There is 2 Data Bundle option.
1.) All Networks Data Bundles
2.) Telkom Mobile Data Bundles
What the difference? Can I buy option 2.) on 8ta sim?
The all networks bundle allows you to roam onto MTN where 8ta does not have coverage and MTN does. The Telkom Mobile bundle allows you to only use the net where telkom mobile has coverage. You can use the bundle on the 8ta sim but check first that you have non-roaming coverage in the areas you frequent.
Cheers