Treat each country as its own project
Mail and files behave much the same wherever a user sits. Telephony does not. Each country has its own regulator, its own rules on numbers and emergency calling, its own carriers and its own contract notice periods. A design that works for head office may be impossible in a country office, and the reverse.
Start with an inventory for each office: the current phone system, who supplies the lines and numbers, the contract end date and notice period, every number in use and what it is for, auto attendants and hunt groups, any fax or alarm lines that someone forgot about, and the quality of the local internet connection. Contract dates often set the timetable more firmly than anything technical.
Talk to each country office lead before you design anything. They know which numbers the public actually rings, which appear on printed materials and partner websites, and which local supplier has been quietly keeping the old system running.
Choose PSTN connectivity per country
Teams Phone connects to the public telephone network in one of a few ways. Microsoft Calling Plans, where Microsoft acts as the carrier. Operator Connect, where a participating carrier provides numbers and connectivity that you manage through the Teams admin centre. Direct Routing, where you or a provider run a session border controller connecting Teams to a carrier of your choice. One tenant can use different options for different users, so you can choose per country.
Availability is the first filter. Calling Plans and Operator Connect are offered in some countries and not others, and the carriers in Operator Connect differ by country. Check Microsoft's current availability list before you design anything. Where neither is available, Direct Routing through a local carrier, or a provider with a presence in that country, is usually the route.
Regulation is the second. Some countries restrict how internet calls may reach the public network, for example by prohibiting toll bypass, which is why Teams offers location-based routing for Direct Routing. Some require a local presence or local documentation to hold numbers. Your carrier or provider in each country should confirm what applies there; do not rely on general advice, including this article.
Operational fit is the third. Calling Plans and Operator Connect leave less infrastructure for you to run, which suits a small central IT team supporting offices in several time zones. Direct Routing gives more control and more choice of carrier, and makes you or your provider responsible for the session border controller and its upkeep.
Moving numbers between tenants
In a consolidation, users move from one or more source tenants into a target tenant, and their numbers need to follow. How that works depends on how each number is provided, so record the provision method for every number during inventory.
Direct Routing numbers sit with your carrier, not with Microsoft. The session border controller is paired with a tenant, so the move is mostly a matter of pairing the controller with the target tenant, assigning numbers to users there and removing them from the source. Plan the cutover carefully so that a number is never live in two tenants at once.
Calling Plan and Operator Connect numbers are held by Microsoft or the operator against a specific tenant. Moving them to another tenant is a porting or reassignment exercise with Microsoft or the operator, not a setting you change yourself. Lead times vary, and some need paperwork from the country office. Raise these requests early, and confirm the current process with Microsoft or your operator before you set dates.
Whatever the method, schedule each country's number move for a quiet period, have the carrier available, and test inbound and outbound calls, including from mobiles and from other countries, before you tell the office it is done.
Emergency calling comes first
Every Teams Phone user who can dial out needs emergency calling that works in their country. With Calling Plans and Operator Connect, numbers are associated with validated emergency addresses held in Teams, so you need an address for each office before numbers are assigned there. With Direct Routing, emergency calls travel through your session border controller and carrier, and routing must be configured to deliver them correctly.
People do not stay at their desks. Dynamic emergency calling uses network information you define for each site, such as subnets and wireless access points, to work out where a caller is. Set it up for each office so that a call from a laptop in a country office reaches the right emergency service with the right location. What is required varies by country, so confirm it with your carrier.
Test emergency calling using the carrier's agreed procedure. Do not test by calling the emergency services without arrangement.
Voicemail, call queues and Exchange Online
Teams voicemail is delivered to the user's Exchange Online mailbox. In a consolidation that creates a dependency: the mailbox must exist and be working in the target tenant before you move the user's number, or voicemail has nowhere to go. Sequence mailbox migration ahead of voice cutover for each office.
Auto attendants and call queues run on resource accounts, which need an appropriate licence before a phone number can be assigned to them. Shared voicemail for an auto attendant or call queue is delivered to a Microsoft 365 group, so create the group in the target tenant and decide who in each office should see it. Rebuild business hours, holiday schedules and greeting languages per country. Public holidays and preferred languages are local, and a greeting in the wrong language is a poor first contact for a beneficiary calling for help.
Dial plans matter too. Staff used to short extensions or local number formats will expect them to keep working. Tenant dial plans with normalisation rules for each country, assigned to the right users, preserve that behaviour and save a surprising number of support calls.
Network and devices
Call quality depends on the local internet connection more than on anything in Microsoft 365. Before you move an office, check bandwidth, latency and the firewall path to Microsoft 365, and whether calls leave the network locally or travel back through head office first. Microsoft publishes network guidance for Teams; work through it for every office, not only the largest.
Where connections are unreliable, plan for it. Forward unanswered calls to mobiles, use simultaneous ring for key roles, and make sure each country office lead knows how to change call forwarding without raising a ticket.
Desk phones, conference phones and common area phones should be certified for Teams, and shared devices need their own account and licence. Check that whatever you choose can be supplied and supported in each country, and that someone local can plug it in and sign it in.
Sequencing and ownership
The sequence below keeps each country's move small and testable. Pilot with one office, ideally the one with the simplest rules and the most patient lead, and carry what you learn into the rest.
Ownership splits naturally. Central IT owns tenant configuration, policies and licensing. Each country office lead owns the local inventory, the local carrier relationship and sign-off after cutover. Finance owns contract notice dates, which are the part of the plan most likely to cost money if they are missed.
Agree a fallback for each cutover: how long the old service stays available, who decides to roll back, and what can realistically be reversed once a number has been ported, which is often less than people assume.
- Inventory each country's telephony, numbers and contracts.
- Confirm the PSTN option, regulatory position and carrier for each country.
- Configure emergency addresses, network sites, dial plans and calling policies in the target tenant.
- Migrate mailboxes before voice for each office.
- Pilot with one office and fix what the pilot finds.
- Move numbers country by country, testing inbound, outbound and emergency calling each time.
- Give notice on old contracts only once the new service is proven.