How to Plan a VoIP Migration for Multiple Office Sites

Migrating a single office to VoIP is relatively straightforward. Migrating five, ten, or fifty sites is a different challenge entirely. Multi-site VoIP migrations involve coordinating internet connectivity, number porting, hardware deployment, and staff training across locations — often with different broadband providers, different legacy phone systems, and different local requirements.

This guide provides a practical framework for planning and executing a multi-site VoIP migration without disrupting business operations.

Why Multi-Site Migrations Need Special Planning

Single-site migrations are relatively forgiving. If something goes wrong, you fix it on the spot. Multi-site migrations compound complexity:

• Each site may have different broadband speeds, providers, and contract end dates.
• Legacy phone systems vary — one site might be on ISDN30 with a PBX, another on analogue lines with standalone phones.
• Number porting timelines differ depending on the losing carrier at each site.
• Staff at remote sites need training and support without your IT team being physically present.
• A failure at one site can affect calls routing to or from other sites.

The key to success is treating the migration as a structured project, not a series of ad-hoc installations.

Phase 1: Site-by-Site Audit

Before designing anything, audit every site individually. For each location, document:

Connectivity:

• Current broadband type, speed, and provider
• Contract end date and any early termination charges
• Whether the connection is suitable for VoIP (run a VoIP quality test)
• Backup connectivity options (4G/5G failover, secondary line)

Telephony:

• Number and type of phone lines (analogue, ISDN2, ISDN30)
• PBX make, model, and age (is it SIP-compatible?)
• All DDI numbers and their allocation (reception, departments, individuals)
• Call volumes — peak concurrent calls, monthly totals, international usage

Devices and services:

• Number and type of handsets needed (desk phones, cordless, conference units)
• Non-voice devices on phone lines (alarms, fax, EPOS, lifts)
• Softphone or mobile app requirements for remote/hybrid workers

Local requirements:

• Site-specific call routing or auto attendant needs
• Local reception or central reception model
• Compliance requirements (call recording, financial services regulations)

Phase 2: Design the Unified Solution

With audit data in hand, design a solution that works across all sites:

Choose a centralised platform. A hosted VoIP platform or Microsoft Teams with Direct Routing provides a single system across all sites. This simplifies management, inter-site calling, and reporting.

Standardise where possible. Use the same handset models, the same dial plan structure, and the same feature set at every site. This reduces training effort and makes support easier.

Plan the dial plan. Design a unified numbering scheme — internal extensions, site prefixes, and DDI allocation — before configuration begins. Changing a dial plan after deployment is disruptive.

Design inter-site call routing. Calls between sites should route internally over the VoIP platform (free) rather than via the PSTN (charged). Ensure the platform supports this natively.

Plan failover. What happens if one site's broadband goes down? Options include automatic failover to mobile apps, 4G backup routers, or rerouting calls to another site. Design this upfront.

Phase 3: Prepare Connectivity

Internet connectivity is the foundation of VoIP. For multi-site migrations:

• Upgrade any sites with inadequate broadband before the phone migration. Do not try to migrate phones and broadband simultaneously.
• Order backup connections (4G routers) for sites where reliability is critical.
• Configure QoS on every router to prioritise voice traffic.
• Test each site's connection with a VoIP quality test after any broadband upgrade.
• If sites are connected by SD-WAN or MPLS, ensure voice traffic is prioritised across the WAN.

Phase 4: Phased Rollout

Never migrate all sites simultaneously. Use a phased approach:

Pilot site (weeks 1–3):

• Choose one site — ideally your head office or a tech-friendly branch.
• Deploy the full VoIP solution, including number porting.
• Run for at least two weeks, gathering feedback on call quality, features, and user experience.
• Document lessons learned and refine the process.

Batch rollout (weeks 4–12+):

• Group remaining sites into batches of two to five, depending on complexity.
• Migrate one batch at a time, with a week between batches for issue resolution.
• Pre-ship hardware and provide remote training before each batch goes live.
• Have your provider or IT team available for same-day support at each go-live.

Final reconciliation:

• Confirm all numbers have ported correctly across all sites.
• Cancel all legacy phone lines and circuits.
• Run a company-wide call quality review after two weeks of full operation.

Phase 5: Post-Migration Management

Once all sites are live:

• Centralise management through a single admin portal. Hosted VoIP platforms and Teams admin centre both support multi-site management from one interface.
• Set up monitoring and alerts for call quality issues at any site.
• Establish a process for adding new sites, onboarding users, and managing number changes.
• Schedule quarterly reviews of call analytics to identify trends, capacity issues, or underused features.

Common Pitfalls to Avoid

• Migrating before broadband is ready. Poor internet equals poor call quality. Always upgrade connectivity first.
• Skipping the pilot. Problems found at one site can be fixed before they affect ten sites.
• Inconsistent configuration. Different dial plans, feature sets, or handset models at each site create ongoing support headaches.
• Underestimating number porting time. Start porting early and allow for delays, especially with smaller regional carriers.
• Forgetting non-voice devices. Alarms, fax, and EPOS on analogue lines need separate migration paths at every site.

For more on enterprise connectivity across multiple locations, see our guide to enterprise VoIP and UCaaS solutions. If your sites use SD-WAN or leased lines, our article on multi-site business connectivity covers the networking side.