SIP Trunking UK | Bridge Your PBX to the Future
Future-proof your existing PBX investment. Connect your legacy hardware to the modern IP network using Stride SIP Trunking—the secure and scalable bridge that eliminates costly ISDN lines and delivers massive call savings.
30-60% cost reduction vs traditional lines
Free remote calling minutes included
2027 PSTN switch-off ready
Setup in 1-2 weeks
What is SIP Trunking and How Does it Replace ISDN?
If your business recently invested significant capital into an on-premise PBX system, you face a dilemma: How do you prepare for the 2027 PSTN Switch-Off without scrapping your expensive hardware? SIP Trunking is the definitive answer.
A SIP Trunk is a virtual communications link that uses the SIP (Session Initiation Protocol) to connect your company’s internal PBX system directly to the external public telephone network (PSTN) via the internet. In simple terms, it is the digital replacement for physical copper wires, such as ISDN or traditional analogue lines.
Instead of paying a massive annual rental fee for a physical ISDN30 line that ties you to a fixed number of voice channels, Stride provides SIP channels—virtual channels delivered over your standard internet connection. This immediately slashes your ongoing telecoms expenditure while retaining the familiar functionality of your existing office phone systems.
If your business recently invested significant capital into an on-premise PBX system, you face a dilemma: How do you prepare for the 2027 PSTN Switch-Off without scrapping your expensive hardware? SIP Trunking is the definitive answer.
A SIP Trunk is a virtual communications link that uses the SIP (Session Initiation Protocol) to connect your company’s internal PBX system directly to the external public telephone network (PSTN) via the internet. In simple terms, it is the digital replacement for physical copper wires, such as ISDN or traditional analogue lines.
Instead of paying a massive annual rental fee for a physical ISDN30 line that ties you to a fixed number of voice channels, Stride provides SIP channels—virtual channels delivered over your standard internet connection. This immediately slashes your ongoing telecoms expenditure while retaining the familiar functionality of your existing office phone systems.
The Anatomy of the Migration
Your PBX was connected via physical ISDN cables to a local exchange.
- The Old Way
Your PBX remains in place, but the ISDN cables are removed. Your system is connected to a VoIP Gateway (if needed) or directly to your LAN. Stride’s SIP Trunk then terminates virtually at your PBX.
- The New Way
The Financial Case: Lowering Costs with SIP Channels
The primary driver for moving to SIP Trunking is the massive operational cost efficiency it delivers. Unlike the upfront capital expenditure (CapEx) required for the PBX itself, SIP Trunking moves your line rental and connectivity costs firmly into the predictable OpEx category.
Eliminating ISDN Rental Fees
Decommission physical lines and replace them with flexible SIP channels, eliminating annual rental fees entirely.
Reduced Call Rates
Bypass traditional carrier tariffs with significantly lower per-minute rates and inclusive bundles.
Reduced Hardware Maintenance
Remove complexity of maintaining external ISDN equipment and reduce reliance on external engineers.
Pay-Per-Channel Scalability
Pay only for the exact number of concurrent channels you need, with instant software-based scaling.
Technical Integration: Connecting Your Existing PBX
SIP Trunking is highly technical and requires specialist knowledge of both IP networking and legacy telephony hardware. Stride’s engineers specialise in ensuring seamless PBX connectivity across all major UK systems.
Compatibility: A Wide Range of Systems
We offer SIP Trunking solutions compatible with the UK’s most common PBX brands:
- Avaya (IP Office, Aura)
- Mitel (MiVoice)
- Cisco (Call Manager)
- Panasonic (KX Series)
- Unify (OpenScape, HiPath)
If your system is less than 15 years old and supports the SIP protocol natively, integration is often a direct, software-only process.
The Role of the VoIP Gateway
For legacy PBX systems that don’t natively support SIP, a hardware intermediary is required.
VoIP Gateway Functions:
- Sits between your legacy PBX (TDM/ISDN) and internet router (SIP/VoIP)
- Translates digital signals into SIP protocol data packets
- Stride engineers handle complete provisioning and configuration
Essential Network Configuration
We work with your IT team to implement QoS (Quality of Service) for prioritising voice data packets and proper firewall configuration for SIP signalling (port 5060) and media transport (RTP ports).
Choosing the Right SIP Trunk Providers UK
Selecting the right partner for SIP Trunking is crucial. You are entrusting your entire external communication flow to the provider’s network architecture. Stride offers key advantages specific to the UK market:
Geo-Redundant UK Infrastructure
SIP Trunks hosted across multiple Tier-1 UK data centres provide unparalleled resilience with automatic failover routing.
Direct Network Peering
Direct connections with major UK operators result in fewer hops, lower latency, and clearer HD call quality.
Dedicated UK Technical Support
UK-based engineers with deep expertise in integrating SIP with legacy hardware from Avaya, Mitel, and other major vendors.
Advanced Features of Modern SIP Trunking
SIP Trunking is not just a replacement for ISDN; it is an upgrade that provides resilience and modern functionality that older TDM technology could never offer.
Enhanced Disaster Recovery
Automatic call redirect to mobile numbers or cloud voicemail if your primary SIP trunk loses registration.
- Instant failover routing
- Maintain business continuity during outages
Comprehensive Number Portability
Seamless migration of your existing telephone numbers—including DDI ranges—with guaranteed integrity.
- Zero-downtime number porting
- Maintain your business identity
Integrated Fraud Protection
Real-time machine-learning fraud detection monitors call volumes and destinations to prevent toll fraud.
- Active monitoring and alerts
- Automatic suspension of suspicious activity
Scalability and Capacity Planning
One of the greatest limitations of legacy ISDN was its fixed capacity. Adding lines required hardware upgrades and engineer visits. SIP Trunking is entirely elastic.
Dynamic Channel Management
Purchase SIP channels based on your maximum concurrent call needs. Scale instantly up or down via the Stride customer portal to optimise costs for seasonal variations.
Understanding Concurrent Calls
Analyse traffic patterns, not headcount. A business with 100 employees may only need 35 SIP channels because not every employee is on the phone simultaneously. We provide detailed traffic reports to ensure you buy exactly the right capacity.
Technical Deployment Process with Stride
Our process is designed to be low-risk and guarantees continuity for your PBX connectivity.
System Audit
Deep analysis of your PBX model, firmware, capacity, and current ISDN usage patterns.
Network Readiness
Testing your internet connection for latency and jitter, with QoS recommendations.
Gateway Configuration
Supply and pre-configuration of VoIP Gateway if required for legacy systems.
Testing & Porting
Internal testing and scheduled number porting with zero downtime switchover.
Frequently Asked Questions: SIP Trunking
The Hybrid Solution: Maximising Your Investment
You don’t need to choose between a costly new system and an outdated, vulnerable one. SIP Trunking provides the perfect hybrid solution, delivering the financial and technical advantages of VoIP while preserving the functionality and investment you have already made in your PBX.
Talk to Stride today, the specialist SIP trunk providers UK businesses trust for complex PBX connectivity.