Teams Voice gets rebuilt in every country
Every country entity has its own PSTN arrangement, its own number ranges and its own regulatory position. Consolidating four voice regions means porting numbers, re-contracting carriers and re-testing emergency calling in each jurisdiction, on timelines the telcos set.
Budget it as its own project with its own critical path. On a recent programme this spanned four countries across Europe and Australasia, and it is the longest-lead item in the whole consolidation.
Power Platform is an inventory problem
Canvas apps, model-driven apps, cloud flows, desktop flows, Power BI workspaces, Forms and Dataverse tables all migrate differently, and none of them are visible from the admin centre in a way you can plan against. PowerShell discovery takes the first fortnight, and you cannot skip it.
Then comes the governance layer that should have existed already: DLP policies, environment provisioning, migration sequencing and licensing discovery. Most estates find premium connector usage nobody knew was licensed.
Move Fabric through Git
Fabric workloads do not move between tenants like documents. Git integration lets you move items in a controlled, reviewable way, and gateway configuration and refresh schedules have to run on both sides while reports are in flight.
Expect a period where the same semantic model exists twice and somebody has to own which one the board pack points at.
The true-up nobody budgeted
Fourteen tenants means fourteen separate agreements, renewal dates and discount positions. Consolidating them usually saves money eventually, but for a while you pay for both the source and target estates.
Model that overlap explicitly. It is typically three to five months per wave, and it is the line item that turns a clean business case into an awkward conversation.