Hi @IBN ,
I'm sorry that my knowledge and experiance may not do much help on questions about the phone system and some questions related with providers. But I find these documents about this process,p lease see if this document could provide any help on your questions:
https://learn.microsoft.com/en-us/MicrosoftTeams/phone-number-calling-plans/port-order-overview#can-i-port-out-my-numbers-from-teams-to-a-different-phone-service-provider-or-carrier
And you may follow the steps here to re-import your numbers to the other Tenants.
https://learn.microsoft.com/en-us/microsoftteams/phone-number-calling-plans/transfer-phone-numbers-to-teams
Also you could call the TSN support for help on these questions.
Hope these could help:)
Best regards,
Lou
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