International Roaming on Magenta Max Plan

Planning on an international trip that has Simply Global Coverage. Following are my questions/doubts:

1. Do incoming calls get charged on cellular network (when abroad) even if they are rejected? (e.g. if the call is originating from USA/country other than USA and gets transferred to voicemail after rejecting)
2. Same question 1 but when on wifi-calling and cellular network off?

3. Can I temporarily turn off voicemail to avoid roaming charges? if yes how?

Basically, I would like to still receive incoming calls while abroad (outside USA) and only get charged for when I receive it?

Would be immense help if anyone has some experience with this?