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Microsoft Teams Phone Integration with a Redstone IP-PBX: What to Consider
Collaboration tools and telephony platforms converged, and most organisations now run two systems that both claim to handle calls. Teams can carry PSTN access through either a carrier connection or direct routing to an operator, while an on-premises IP-PBX brings trunks, recording, queue logic, and physical endpoints. The integration question is not whether the two can coexist, but which system is authoritative for which call type.
Two Integration Models, Fundamentally Different
| Aspect | Teams call control / hybrid | Teams direct routing |
|---|---|---|
| Signalling path | IP-PBX controls calls, Teams presents them | Operator connects directly to Teams, PBX bypassed |
| Recording location | PBX recording, as today | Separate recording arrangement needed |
| Queue and IVR behaviour | Existing PBX logic retained | New configuration required |
| Physical handsets | Continue to work through PBX | Not part of the call path |
| Line management | Change once in PBX | Change in Teams and in the operator portal |
| Operational complexity | Lower | Higher, two systems to keep aligned |
The Double Registration Problem
When the same extension identity exists in both the PBX and Teams, calls can arrive twice, presentation can duplicate, and users can end up answering on two devices. The fix is not to avoid integration, but to make the extension-to-identity mapping explicit and testable. Where a physical handset and a Teams client both need the same user identity, the deployment should confirm how concurrent registration is handled before users are migrated, not after.
Deciding Which System Owns Which Call
- Calls to and from external PSTN numbers generally belong on the PBX when recording, queue, and trunk control are business requirements
- Internal collaboration between platform users generally belongs in Teams
- Call recording compliance should have one authoritative location, not two partial ones
- Emergency calling configuration should not depend on which client placed the call
- Line moves, numbering changes, and site additions should have one system of record
Sequencing the Migration
Most successful programmes move in stages. Pilot users or one site first. Confirm calling, presence, recording, and voicemail behaviour before expanding. Keep the PBX authoritative for PSTN throughout, so the risk is contained to a small user group while the integration is proven.
Things that commonly go wrong in a pilot
- Dual registration causing duplicate ring on desk phone and Teams client
- Voicemail diverging between systems, so callers reach a dead end
- Recording gaps for calls that bypass the PBX entirely
- Contact centre queue behaviour differing between the two clients
- Directory and presence information drifting out of alignment
What to Ask Before Committing
- Which system will be authoritative for PSTN trunks and recording for the whole estate?
- How will concurrent desk phone and Teams registration be handled?
- What is the fallback if the collaboration service is unavailable but PSTN must still work?
- Who owns numbering changes between the two systems?
- How does the plan handle sites in different countries with different emergency calling contexts?
Redstone Position
Redstone IP-PBX platforms remain the system of record for PSTN, recording, and physical endpoints in hybrid estates. That keeps business-critical telephony behaviour, compliance obligations, and multi-site numbering under one platform while collaboration tooling is introduced around it. Redstone assists with integration design so that calling, recording, and routing behaviour is verified end to end before user groups are migrated.
Redstone can provide an integration plan covering trunk ownership, recording placement, extension mapping, and a staged pilot sequence for organisations introducing Teams alongside an existing IP-PBX.
Redstone Systems, Inc. founded in Delaware, USA in December 2002, has been the ODM vendor for many well-known communications companies, serving the Southeast Asian market. In 2020, Redstone Systems will begin to return to the North America market with its self-developed brand.
Redstone has a complete product line of intelligent voice gateways, providing IP-PBXs, analog VoIP gateways (FXS/FXO), digital VoIP gateways (E1/T1), border appliances, and session boundary controllers (SBCs).
With advanced technology in digital signal processor (DSP), speech coding and speech processing, as well as efficient operational tools such as cloud remote management, auto provisioning, Redstone gateways are widely used in markets of enterprise communications, cloud communications, call centers, operators’ IMS/SIP trunks, bringing users friendly, efficient and reliable communication experience.
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