For any communication outside Fiverr you’ll have to get permission from CS.
I’d highly discourage you doing so as any call/message will not be billable and therefore you’ll invest a chunk of your time for free.
Also anything discussed outside of Fiverr cannot be verified on a possible arbitration.
I’ve had clients which want me to do the same and I told them that as a freelancer I expect my time to be compensated so if they wish to schedule a call they could place an order, or alternatively they can record themselves and send me the file so I can revise it at my own time.
Being available at different timezones can be though and it’s not worth in my opinion, but if you decide to do so make sure to get permission from CS beforehand.