How to Migrate Your PBX to VoIP: Complete Guide

PBX vs PABX: Clearing Up the Terminology

Before we dive into the migration process, let us clear up a common source of confusion. You may see the terms PBX and PABX used interchangeably — and that is because they effectively mean the same thing.

• PBX — Private Branch Exchange. A private telephone system used within a business that connects internal extensions to external phone lines
• PABX — Private Automatic Branch Exchange. The same thing, but with the word "Automatic" added to distinguish it from the very early manual switchboards that required a human operator to connect calls

In modern usage, every PBX is automatic, so the terms are interchangeable. Whether your system is labelled PBX or PABX, the migration process is the same. Common PBX/PABX systems in Northern Ireland include Avaya IP Office, Panasonic NS700/NSX/TDA, Mitel, NEC, Samsung, and Siemens/Unify.

Understanding Your Two Migration Paths

Every business migrating from a traditional PBX to VoIP has two fundamental options. The right choice depends on your current system, your budget, and your long-term plans.

Path 1: SIP Trunking — Keep Your PBX, Replace the Lines

SIP trunking replaces your ISDN or analogue phone lines with internet-based voice connections. Your PBX system stays exactly where it is — only the lines coming into it change. Think of it as swapping the road that leads to your building while the building itself remains untouched.

Best for: Businesses with a working PBX that they are happy with, businesses wanting the fastest and cheapest migration, and businesses that want to buy time before a full replacement.

Path 2: Hosted VoIP — Replace Everything with Cloud

Hosted VoIP removes the PBX entirely and moves your phone system to the cloud. No on-premise hardware to maintain — everything is managed by your VoIP provider in their data centres.

Best for: Businesses with aging PBX systems, businesses wanting modern features (mobile apps, CRM integration, call recording), and businesses wanting to eliminate all on-premise telephony hardware.

Step-by-Step: The PBX to VoIP Migration Process

Whether you choose SIP trunking or hosted VoIP, the migration follows a structured process. Here is exactly what happens at each stage:

Step 1: Audit Your Current System

Before anything changes, we need a complete picture of what you have today. The audit covers:

• PBX identification — What make and model is your PBX? What software version is it running? How old is it? What condition is the hardware in?
• Line inventory — How many ISDN30 PRI channels, ISDN2e BRI channels, and analogue lines do you have? What is each line used for?
• Extension count — How many extensions are in use? How many handsets (digital, IP, DECT cordless)?
• Call flow mapping — How are incoming calls routed? What hunt groups, auto-attendants, and voicemail boxes are configured?
• Phone numbers — What numbers do you have? Which are main numbers, which are DDIs (direct dial-in), which are fax numbers?
• Analogue devices — Are there fax machines, alarm systems, lift phones, door entry systems, or card terminals connected to analogue lines?
• Special requirements — Call recording, call centre features, CRM integration, Microsoft Teams, remote workers?

This audit is the foundation of the entire migration. Skip it or rush it, and you risk missing lines, losing features, or causing disruption on go-live day.

Step 2: Assess Your Broadband

VoIP runs over your internet connection, so your broadband needs to be up to the job. Here is what you need:

• Bandwidth per call — Each simultaneous VoIP call requires approximately 100Kbps of bandwidth in each direction (using the G.711 codec). A business with 10 concurrent calls needs at least 1Mbps upload and 1Mbps download dedicated to voice
• Minimum recommendation — For most small businesses (up to 20 users), we recommend a minimum of 10Mbps symmetrical broadband. For larger businesses or those with heavy data usage alongside voice, a dedicated leased line is advisable
• Quality of Service (QoS) — Your router should be configured to prioritise voice traffic over data traffic. This prevents large file downloads or video streaming from degrading call quality
• Latency and jitter — VoIP is sensitive to network latency (delay) and jitter (variation in delay). Latency should be under 150ms and jitter under 30ms for acceptable call quality. Most modern broadband connections in Northern Ireland meet these requirements
• Failover — Consider what happens if your broadband goes down. Options include 4G failover routers, dual broadband connections, or mobile app fallback

If your current broadband is not sufficient, factor in the time and cost of an upgrade. A business broadband upgrade or leased line installation can take 4-12 weeks depending on your location and provider.

Step 3: Choose Your Migration Path

Based on the audit results, choose between SIP trunking and hosted VoIP:

Step 4: Provision SIP Trunks or Hosted VoIP Platform

Once the path is chosen, the technical provisioning begins:

• For SIP trunking — SIP trunk accounts are created with a reliable UK VoIP provider. Trunk credentials, codec settings, and channel counts are configured. This typically takes 1-3 business days
• For hosted VoIP — User accounts are created on the hosted platform. Call flows, hunt groups, auto-attendants, and voicemail are configured to match your existing setup. New IP handsets are ordered and pre-configured. This typically takes 1-2 weeks

Step 5: Port Your Phone Numbers

Number porting is the process of transferring ownership of your phone numbers from your current provider (typically BT/Openreach) to your new VoIP provider. This is a critical step:

• Timeline — Number porting typically takes 2-4 weeks from submission to completion. Complex ports (large number ranges, multiple providers) can take longer
• No number changes — Your customers continue calling the same numbers they always have. The port is invisible to callers
• Porting day — On the agreed porting date, your numbers are switched from the old provider to the new one. This is coordinated to minimise any gap in service — typically a few minutes at most
• DDI ranges — If you have a range of DDI (direct dial-in) numbers, the entire range is ported together

Step 6: Configure and Install

With SIP trunks provisioned and numbers ready to port, the physical migration takes place:

• For SIP trunking — An engineer configures the SIP trunk on your PBX. For Avaya IP Office, this is done via Avaya Manager software. For Panasonic NS700, via the web interface. The ISDN cards are removed or deactivated. All call routing is configured to use the new SIP trunk
• For hosted VoIP — New IP handsets are deployed to every desk. The hosted platform is configured with all call flows, hunt groups, and features. Softphone apps are installed on mobile devices and computers. The old PBX is decommissioned

Step 7: Test Everything

Testing is not optional — it is the most important step in the entire migration. We test:

• Incoming calls to every phone number — do they ring the correct destination?
• Outgoing calls — does the correct caller ID display?
• Hunt groups — do calls distribute correctly across the group?
• Voicemail — do messages record and deliver correctly?
• Auto-attendant — do menu options route to the correct destinations?
• Call transfer — can calls be transferred between extensions?
• Conference calling — do multi-party calls work?
• Fax (if applicable) — does fax-over-IP or email-to-fax work?
• Emergency calls — can 999 calls be made successfully?
• Call quality — are calls clear with no echo, delay, or distortion?

Step 8: Go Live and Monitor

Once testing is complete and everything is confirmed working, the system goes live. We monitor closely for the first 48-72 hours to catch any issues that only appear under real-world call volumes. Any adjustments to call routing, codec settings, or QoS configuration are made during this period.

Common Pitfalls to Avoid

Having completed hundreds of PBX to VoIP migrations across Northern Ireland, we have seen every mistake in the book. Here are the most common pitfalls and how to avoid them:

• Forgetting analogue lines — Businesses focus on the main phone system and forget about fax machines, alarm systems, lift phones, and card terminals connected to analogue lines. Every line must be identified and migrated. See our ISDN switch-off guide for a complete list of analogue devices to check
• Inadequate broadband — VoIP requires reliable bandwidth. If your broadband is slow, congested, or unreliable, call quality will suffer. Assess and upgrade your broadband before migrating voice traffic onto it
• No QoS configuration — Without Quality of Service settings on your router, a large file download can degrade call quality for everyone in the office. QoS prioritises voice packets over data packets
• Rushing number porting — Number porting has a fixed timeline. Trying to rush it leads to errors, rejected port requests, and delays. Start the process early
• Insufficient testing — Going live without thorough testing is a recipe for disaster. Test every number, every hunt group, every feature before declaring the migration complete
• No failover plan — If your broadband goes down, your phones go down. Plan for this with 4G failover, dual broadband, or mobile app fallback
• Ignoring staff training — If you are deploying new handsets or a new system, staff need training. Even a 30-minute session prevents confusion and support calls on day one

Migration Timeline: What to Expect

Here are realistic timelines for each migration path:

SIP Trunking Migration (Keep Your PBX)

• Week 1 — Audit and assessment
• Week 1-2 — SIP trunk provisioning and number porting submission
• Week 3-4 — Number porting completes, SIP trunk configured on PBX, testing
• Week 4 — Go live
• Total: 3-4 weeks (the actual on-site work is typically 1 day)

Hosted VoIP Migration (Replace Your PBX)

• Week 1 — Audit and assessment
• Week 1-2 — Platform configuration, handset ordering, number porting submission
• Week 2-3 — Handset deployment, staff training
• Week 3-4 — Number porting completes, final testing, go live
• Total: 3-4 weeks for standard deployments, 4-8 weeks for larger or complex migrations

Cost Savings After Migration

Most businesses save significant money after migrating from PBX/ISDN to VoIP. Here is where the savings come from:

• Line rental savings — SIP trunks cost £3-8 per channel vs £15-25 per ISDN channel. A 30-channel migration saves £300-500 per month in line rental alone
• Call cost savings — VoIP call rates are typically lower than ISDN, especially for international calls. Many hosted VoIP plans include unlimited UK calls
• Maintenance savings — Hosted VoIP eliminates PBX maintenance contracts, which can cost £1,000-5,000 per year for Avaya and Panasonic systems
• Hardware savings — No more PBX expansion cards, replacement parts, or hardware upgrades
• Flexibility savings — SIP trunks can be provisioned in any quantity (not locked into 30-channel ISDN increments), so you only pay for what you need

Why Choose Drakos Systems for Your PBX Migration

• Avaya and Panasonic specialists — 20+ years of experience with the most common PBX systems in Northern Ireland
• Belfast-based engineers — On-site support across all of NI
• End-to-end service — From initial audit through to go-live and ongoing management
• Both paths available — SIP trunking or hosted VoIP, with honest advice on which is right for you
• ISO 27001 certified — Information security independently audited
• Proven track record — Hundreds of successful migrations across Northern Ireland

Frequently Asked Questions