Why Enterprises Are Replacing Legacy PBX With Cloud VoIP
A legacy PBX (Private Branch Exchange) is an on-premise telephone switch that routes calls inside a building and connects them to the public network over fixed lines. A cloud VoIP system does the same job as software in a data center, reaching handsets and apps over the internet.
The difference that matters is where capacity lives. With a PBX, channel capacity is a physical property of a box you own. With cloud VoIP, it is a setting.
Why are enterprises migrating away from on-premise PBX?
Four reasons come up repeatedly in migrations we run:
- Capacity is fixed. A PBX sized for 200 extensions needs a hardware purchase to reach 220. Cloud capacity changes in the admin console.
- Remote work breaks the model. A PBX assumes the user is inside the building. Supporting home workers means VPNs or forwarding chains that degrade audio and hide call data.
- Maintenance is specialized. Replacement cards for discontinued systems come from resellers, and the engineers who configure them are retiring faster than they are replaced.
- Resilience is single-site. If the building loses power or connectivity, the phone system goes with it.
What does cloud VoIP actually change?
| Legacy PBX | Cloud VoIP | |
|---|---|---|
| Adding capacity | Hardware purchase, site visit | Admin console, minutes |
| Remote users | VPN or call forwarding | Native, any device |
| Failover | Second site, duplicated hardware | Geo-redundant by default |
| Upgrades | Scheduled engineer visit | Continuous, no downtime |
| Call data | Local CDR export | Real-time analytics and API |
| Capital cost | Large up-front | Per user, per month |
How much bandwidth does a cloud phone system need?
Less than most teams assume. Salamtalk uses the Opus codec at roughly 50 kbps per concurrent call. A 50-person office where a third are on the phone at once — about 17 concurrent calls — needs under 1 Mbps for voice.
The constraint is almost never raw bandwidth. It is jitter and packet loss. Voice is sensitive to variance in packet arrival, not volume, so prioritize voice traffic with QoS rather than buying a larger circuit.
Can we keep our existing phone numbers?
Yes. Number porting moves your existing local, toll-free and international numbers to the new provider. Salamtalk ports at no cost, and numbers stay live throughout — the cutover is a routing change, not a disconnection.
Porting timelines are set by the losing carrier, not the gaining one. Local US numbers typically complete in 2–4 weeks; international varies by country.
Will our existing desk phones work?
In most cases, yes. Standard SIP handsets from Poly, Yealink and Cisco are compatible and can be re-provisioned to point at the new platform. Proprietary digital handsets tied to a specific PBX vendor generally cannot be reused.
This matters for migration cost: re-provisioning existing SIP phones is a configuration change, while replacing proprietary handsets is a per-desk hardware purchase.
What does a migration look like in practice?
A low-risk cutover runs in parallel rather than as a single switch:
- Audit current extensions, call flows, IVR menus and integrations.
- Provision the cloud platform alongside the PBX — both run at once.
- Pilot with one team, using new numbers, for one to two weeks.
- Port main numbers once the pilot is stable.
- Decommission the PBX after a quiet period, typically 30 days.
The PBX stays available as a fallback until the final step, which is what keeps downtime at zero.
How should we secure voice traffic after migrating?
Encrypt both layers. Signalling should run over TLS 1.3 and media over SRTP. Unencrypted SIP on a public network is readable in transit.
Also enable STIR/SHAKEN caller authentication, which cryptographically attests caller ID and is required for US carriers. See our VoIP security and compliance page for the full control set.
Is cloud VoIP cheaper than a PBX?
Usually, but the saving is rarely in the per-minute rate. It comes from removing maintenance contracts, site visits, hardware refresh cycles and the second site kept for failover.
Compare total cost over five years, including the hardware refresh a PBX will need in that window, rather than comparing monthly line rental.
Next steps: see business VoIP for the platform overview, SIP trunking if you want to keep your current PBX and replace only the lines, or pricing for per-user plans.