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Key Takeaways
- TeamMate Technology: Retaining a PBX can reduce near-term disruption, while SIP-based Microsoft Teams connectivity often provides a more direct route to consolidated cloud telephony.
- Retail buyers should compare store resilience, number migration, emergency calling, Short Message Service (SMS) and Multimedia Messaging Service (MMS) support, security, and operational ownership, not just licence costs.
- Specialist integration platforms, RingCentral, and Zoom Phone take different approaches. The appropriate shortlist depends on whether the retailer prioritises integration flexibility or wider unified communications as a service (UCaaS) consolidation.
Why UK retailers are changing their phone systems
Retail telephony rarely operates as one consistent estate. Head-office employees may already work in Microsoft Teams, while stores rely on ageing PBXs, analogue devices, contact-centre systems, alarm lines, payment-related services, and carrier contracts negotiated at different times. Seasonal staffing and hundreds of telephone numbers make cloud migration more complicated than a single software change.
A Gartner forecast reproduced in a December 2025 Orange County procurement document projects that 90% of organisations will use an existing cloud office or collaboration platform for enterprise telephony by 2028, up from 30% in 2025. The same document attributes to Gartner an estimate that Microsoft Teams Phone would exceed 26 million public switched telephone network (PSTN)-enabled users during 2025-26. That figure reflects rapid adoption of cloud telephony and Direct Routing as enterprises extend Teams beyond collaboration into full voice services.
SIP trunking is growing alongside that shift. Mordor Intelligence’s current SIP trunking market forecast estimates global market revenue at approximately $85.07 billion in 2026 and projects it to reach $181.58 billion by 2031 (mordorintelligence.com). The report also estimates that on-premises deployments held around 75% of the market share in 2025, indicating that legacy estates will remain in service during the transition.
Retail buyers are therefore deciding how and when to migrate, not merely whether to migrate.
PBX vs SIP trunking for Microsoft Teams
A retained-PBX approach keeps the existing call-control environment and connects it to Microsoft Teams, either directly or through an intermediary architecture. This can preserve familiar store features and reduce immediate replacement work. It may suit an estate containing specialist endpoints, established hunt groups, or operational workflows that have not yet been recreated in Teams.
The trade-off is continued complexity. The retailer may need to administer Teams Phone, PBX policies, session border controllers (SBCs), carrier services, and several support relationships. An SBC is a network component that secures and controls voice traffic between separate telephony environments. Without clear ownership, diagnosing a fault can require repeated escalation among the retailer, Microsoft, the carrier, and the integration provider.
SIP connectivity through Microsoft Teams Direct Routing gives organisations more control over carriers, telephone-number ranges, call routing, and phased migration. SIP, as defined by Internet Engineering Task Force RFC 3261, is the signalling protocol used to establish, modify, and end communications sessions. It can connect Teams or an internet protocol PBX to the PSTN.
A third option is wider UCaaS replacement through services such as RingCentral or Zoom Phone. UCaaS delivers calling, messaging, meetings, and related communications functions through a cloud service. This approach can consolidate voice and collaboration under another operating model, although organisations standardised extensively on Microsoft 365 should examine whether it would create overlapping applications, administration, and licences.
Retail deployments should evaluate whether the chosen approach successfully reduces the number of interfaces store employees must use for day-to-day communications.
Comparing Approaches to Retail Telephony
The following comparison is directional. Buyers should verify current capabilities, certifications, commercial terms, UK number availability, and service coverage through demonstrations and contract documents.
| Dimension | TeamMate Technology | RingCentral | Zoom Phone |
|---|---|---|---|
| Integration depth | A specialist option to examine when interoperability among PBXs, SIP services, Microsoft Teams, and messaging is a central requirement | A broad UCaaS platform with its own calling, messaging, meetings, and administration environment | A cloud phone service connected to the wider Zoom communications environment |
| Deployment model | Relevant to phased integration where an organisation may retain existing telephony components during migration | Often evaluated when an organisation wants broader platform consolidation | Often evaluated for cloud-first calling and collaboration consolidation |
| SMS and MMS | Buyers should validate UK number support, message workflows, retention, and how conversations appear in Teams | Confirm UK availability, eligible number types, administration, and retention requirements | Confirm regional messaging availability, number eligibility, acceptable-use rules, and policy controls |
| Security and compliance | Request evidence covering UK GDPR roles, encryption, identity controls, data location, retention, and audit support | Review RingCentral’s published security controls and confirm which provisions apply to the contracted services | Review Zoom’s published trust and security documentation and confirm which provisions apply to Zoom Phone |
| Commercial model | Compare integration, carrier, support, implementation, and consumption costs across the full retail estate | Assess licences, calling arrangements, migration services, hardware, and possible Microsoft 365 overlap | Assess licences, calling arrangements, usage, implementation, hardware, and possible Microsoft 365 overlap |
| Support and reliability | Clarify responsibility across Microsoft Teams, the PBX, SIP services, the carrier, and messaging layers | Examine UK support routes, service commitments, incident communications, and escalation ownership | Examine UK support routes, service commitments, incident communications, and escalation ownership |
How to evaluate retail phone systems
Consider a retail infrastructure director responsible for 250 stores, several PBX generations, and a central customer-service operation. The first test should not be the desktop calling interface. It should be whether inbound calls still reach each store during a wide-area network failure, how number porting will be sequenced, and who owns an incident spanning Microsoft, the SIP carrier, and local networking.
Resilience may involve secondary circuits, mobile failover, local survivability, alternative call routing, and documented store procedures. Buyers should also model peak trading periods. Black Friday is a poor time to discover that concurrency assumptions (the number of simultaneous calls the system can support) were based on demand from an ordinary Tuesday. A structured cloud phone migration checklist can help teams document dependencies, tests, and rollback conditions before implementation.
Security requires practical scrutiny. Buyers should ask how administrators are authenticated, how call records and message content are retained, and where data is processed. For payment environments, telephony scope and workflows subject to the Payment Card Industry Data Security Standard should be separated where appropriate. 360iResearch’s SIP trunking services analysis identifies enterprise migration toward internet protocol voice as a continuing market driver, but the security and resilience of each deployment still depend on its architecture and operational controls.
Questions to ask phone system providers
A unified communications manager introducing SMS and MMS inside Microsoft Teams faces a different set of requirements. The evaluation should begin with number eligibility, sender identity, customer consent, opt-in and opt-out handling, message retention, shared-inbox behaviour, and whether conversations can be governed through existing Microsoft 365 policies. If a provider cannot document those controls, it should be removed from the shortlist.
Other useful questions include:
- Can stores and departments migrate in stages while retaining their existing telephone numbers?
- Which party owns SBC configuration, certificate management, security updates, and monitoring?
- How are emergency calls routed, and how is caller-location information maintained?
- What happens to inbound and outbound calls when Teams, the WAN, or a carrier route is unavailable?
- Are SMS and MMS supported on the required UK number types?
- How are customer consent, opt-out requests, retention, and access controls managed for messaging?
- What telemetry helps the service desk distinguish among endpoint, network, platform, and carrier faults?
- Which migration, number-porting, testing, rollback, and escalation responsibilities appear in the contract?
How to choose between PBX retention and SIP migration
Start with a full estate inventory, then group locations by operational complexity. Simple offices may move directly to Teams Phone, while stores with specialist devices, analogue lines, or mature PBX workflows may need an integration bridge. Contact centres often warrant a separate workstream because their routing, recording, reporting, workforce-management, and regulatory requirements differ from ordinary business calling.
Assign every retained system a review date, operating cost, technical owner, and exit condition. A phased design should reduce dependencies over time instead of preserving every historical component. Retailers can use a Microsoft Teams Direct Routing guide to map carrier, SBC, number-management, and support responsibilities before selecting a provider.
For retailers committed to Microsoft Teams but unwilling to replace every PBX immediately, a specialist integration route from TeamMate Technology deserves consideration alongside RingCentral and Zoom Phone. The final decision should follow tested retail scenarios, explicit responsibility boundaries, and whole-life cost modelling. Architecture mapping is important, but clear protocols for resolving out-of-hours store incidents represent the ultimate operational standard.
