To enable integration between Teams and your PBX using our service you will be using a Microsoft feature called Teams Direct Routing. This becomes available with the Phone System licence. The Phone System Licence itself is what enables the Dial Pad in Teams and allows calls to be made via Teams.
Generally speaking the Phone System Licence is an add-on to all Office 356 plans but is included in the E5 plan. Microsoft may alter plans from time to time but the diagram below, should help in understanding which licences you will require in your Office 365 account.
Using the options below, the customer does not need to change any of their current licence levels for Microsoft 365.
Microsoft Phone System is also available on a 1-month free trial for 25 users to allow customers to evaluate the full calling experience of Teams.
Note: When purchasing the Microsoft 365 Business Voice plan, be sure to purchase the version "Without calling plan". This is not available in the Microsoft Portal; this lower cost SKU generally has to be purchased through a Microsoft Licencing Distributor.
In any case do not purchase 'Calling Plans' these are Microsoft minutes & numbers bundles, the phone service you are connecting already has this.