Moving from an on-premises PBX to a hosted phone system removes patching, SIP trunk firewall rules and hardware failures from your list, but a rushed switch loses calls. To migrate PBX to cloud safely, treat it like any server migration: inventory everything, test in parallel, cut over at a planned time and keep a rollback path until numbers have ported. The plan below works whether you are leaving 3CX, FreePBX or plain Asterisk.
Short answer: Export the extension list, ring groups, queues, IVR menus, business hours and DIDs from the old PBX; check upload bandwidth, QoS and outbound firewall rules at every site; build the same call flows in the new system and pilot with one team using temporary numbers; then submit number porting, forward calls during the port window, and keep the old PBX and its call records until every number has moved and been tested.
Table of Contents
1. Inventory the old system
List extensions and users, ring groups, queues, IVR menus with their prompts, time conditions, voicemail boxes, call recording rules, every DID and which route it hits, and integrations such as CRM click-to-call. Do not forget analogue lines on ATAs: fax machines, door entry, lift phones and alarm diallers often need special handling or a dedicated line.
# FreePBX / Asterisk: quick exports
fwconsole bi --export extensions > extensions.csv
asterisk -rx "pjsip show endpoints" > endpoints.txt
mysqldump asteriskcdrdb > cdr-backup.sql
tar czf recordings.tgz /var/spool/asterisk/monitorOn 3CX take a full backup from the admin console and export the user list and call reports before you begin.
2. Choose the platform
Compare how each provider handles the features your inventory shows you rely on: call queues, IVR, CRM integration, call recording retention, local numbers in your countries and per-user pricing. Our reviews of JustCall and CloudTalk cover plans, prices and limits, and the JustCall vs CloudTalk comparison puts them side by side.
3. Check the network
Size upload bandwidth for concurrent calls (the VoIP codec bandwidth guide has the figures), enable QoS on the edge router, disable SIP ALG, and allow the provider’s outbound HTTPS and UDP media ranges if your firewall filters outbound traffic. Measure jitter and loss from each site with the checks in the VoIP call quality guide.
4. Rebuild call flows
Recreate ring groups, queues, IVR and business hours in the new system from your inventory. Record fresh prompts rather than reusing old low-bit-rate files, and write down every routing decision so it can be tested line by line.
5. Pilot with one team
Give one team the new apps or desk phones with temporary numbers for a week. Test inbound, outbound, transfers, voicemail to email, recording, and mobile apps on 4G. Fix issues before anyone else moves.
6. Port the numbers
Submit porting requests with the latest bill from the current carrier; names, addresses and account numbers must match exactly. Porting takes days to weeks depending on country and carrier, so plan the cutover date around the confirmed port date. The phone number porting guide lists the documents and common rejections.
7. Cut over
On port day, change the old PBX’s inbound routes to forward to the new temporary numbers as a safety net, then test every ported DID as it goes live. Keep the old system running and registered until the last number is confirmed.
8. Decommission carefully
Export call detail records and recordings you must retain for compliance, cancel old SIP trunks only after porting completes (cancelling first can release the numbers), remove the SIP firewall rules, and wipe the old server’s disks.
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Migrate PBX to cloud at a glance
Official documentation: 3CX documentation, Asterisk documentation, FreePBX documentation.
Related guides: Port a phone number to VoIP · VoIP codec bandwidth · VoIP call quality.
Frequently asked questions
How long does a PBX to cloud migration take?
For a single office with up to about 50 users, plan two to six weeks. Most of that time is number porting; the technical build and pilot usually take a few days.
Can I keep my existing desk phones?
Often yes, if the new provider supports your phone model for provisioning. Otherwise switch users to the desktop and mobile apps, which avoids provisioning work entirely.
What happens to calls during number porting?
The number stays with the old carrier until the port completes, then switches within minutes to hours. Keep the old PBX active and forward to temporary numbers so no calls are lost if the switch is delayed.
Maintenance record
This guide changes servers, data or security settings, so we re-check it against current versions on a fixed schedule. Take a backup or snapshot before you start.
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- Sources
- docs.asterisk.org