The reason is some countries do not support Business Voice with Calling Plan.
In countries and regions without support for Calling Plans, you need to purchase Business Voice from a Microsoft partner or reseller. They will work with your third-party telephone provider to set up Direct Routing between your on-premises telephony hardware and Microsoft 365.If your tenant is located in a country or region that doesn't support Calling Plans, check out Get help from a Microsoft reseller or partner.
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