Choosing the right voice system for your business used to be straightforward: order a few phone lines, install a PBX box, and you were ready to go. Today, the options are far more powerful — and more complex.
With the rise of cloud communications, businesses now have multiple routes to connect their people and customers: SIP trunks, hosted PBX systems and Microsoft Teams Phone are the three most common. Each offers unique advantages, costs and technical considerations. The key is understanding which one aligns best with your business goals, structure and existing IT environment.
The end of traditional telephony
The era of traditional ISDN phone lines is ending fast. In Ireland and across Europe, carriers are phasing out ISDN networks by 2027, forcing businesses to migrate to IP-based alternatives. This shift isn't just regulatory — it's strategic. Voice over IP (VoIP) systems offer lower costs, greater flexibility and more integration potential than legacy lines ever could.
"This is the biggest communications shift since the mobile revolution. Every Irish business — large or small — will need to choose their next-generation voice platform within the next two years."
Gary Melvin, CTO, Nostra
What is SIP trunking?
SIP (Session Initiation Protocol) trunks replace traditional phone lines with virtual connections over the internet, allowing your existing on-site PBX to make and receive calls via your internet connection.
Advantages:
- Lower call costs — VoIP calls are cheaper, especially for international traffic
- Scalability — add or remove lines instantly without new physical circuits
- Resilience — redundant SIP links keep services live even if one route fails
- Integration — works with legacy PBXs, allowing a phased migration to the cloud
Considerations: it requires robust, business-grade connectivity, still depends on on-premises PBX hardware and maintenance, and disaster recovery depends on local infrastructure resilience.
"SIP trunking is a brilliant transitional solution for organisations that want flexibility and cost savings without ripping out their existing systems."
Darren Mooney, Head of Security, Nostra
What is hosted PBX?
A hosted PBX moves your phone system into the cloud. Instead of managing physical servers and lines, everything runs virtually from a secure data centre. Users connect via desk phones, softphones or mobile apps, and all routing, voicemail and call features are handled in the cloud.
Advantages:
- No on-site hardware — everything is cloud-managed and maintained
- Scalable and flexible — add or remove users and features instantly
- Lower upfront costs — pay per user, per month
- Resilient and redundant — built-in failover across multiple data centres
Considerations: voice reliability needs strong, stable internet connections; customisation varies between providers; integration with Microsoft 365 or Teams requires additional configuration.
"Hosted PBX makes sense for businesses that want simplicity and predictable costs. It's ideal for multi-site operations or hybrid teams that need the same experience everywhere."
Reg Stallard, Cyber Risk Consultant, Nostra
What is Microsoft Teams Phone?
For organisations already using Microsoft 365, Teams Phone has become the natural evolution of business telephony. It transforms Teams into a full phone system — complete with direct dial numbers, call queues and conferencing — all within the familiar Teams interface.
Advantages:
- One platform for everything — chat, video and voice in a single app
- Remote and hybrid work ready — accessible from any device or location
- Deep Microsoft 365 integration — calendar, contacts and files unified
- Enterprise security and compliance — managed under Microsoft's global standards
Considerations: it requires Teams Calling Plans or SIP integration via Direct Routing; audio quality depends heavily on network design and QoS; complex call-centre requirements may need add-ons or hybrid setups.
"Teams Phone is incredibly powerful — but it's only as good as the network beneath it. Without proper design and voice optimisation, even Teams can struggle."
Gary Melvin, CTO, Nostra
Comparing the options side by side
| Feature | SIP trunking | Hosted PBX | Teams Phone |
|---|---|---|---|
| Deployment | Hybrid (uses existing PBX) | Fully cloud-based | Cloud-based (via Microsoft 365) |
| Best for | Enterprises with existing PBXs | SMEs and distributed teams | Microsoft 365 environments |
| Scalability | Moderate | High | Very high |
| Cost structure | Per trunk/channel | Per user/month | Per user/month |
| Hardware | On-prem PBX required | None | None |
| Redundancy | Dependent on setup | Built in | Built in |
| Integration | Legacy PBX, UC tools | CRM, softphones | Microsoft 365, Teams, Outlook |
| Migration path | Step toward full cloud | Full cloud now | Cloud-first strategy |
How to choose
Choose SIP trunks if you've recently invested in an on-site PBX and want to extend its life, need gradual migration without disruption, or want full control of your system while reducing call costs.
Choose hosted PBX if you want to remove hardware management entirely, run multiple sites or a hybrid workforce, or need simple scaling and predictable monthly costs.
Choose Teams Phone if you already use Microsoft 365 company-wide, want unified collaboration across chat, video and voice, and need enterprise-grade security and global connectivity.
"Most enterprises we work with adopt a hybrid approach — starting with SIP for flexibility, then moving to hosted PBX or Teams when their infrastructure is ready."
Darren Mooney, Head of Security, Nostra
The Irish context: network quality is the decider
In Ireland, the choice often comes down to connectivity quality. Urban businesses with fibre availability can easily deploy cloud voice solutions. In more rural regions, where bandwidth or latency issues persist, SIP trunking can provide a safer interim step.
"Voice depends on consistent bandwidth and proper QoS. If your network isn't optimised for it, the best cloud phone system in the world will still underperform."
Reg Stallard, Cyber Risk Consultant, Nostra
That's why Nostra Connect pairs voice services with enterprise-grade data connectivity — designed, monitored and managed as one complete system.
Looking ahead: convergence and flexibility
The future of voice isn't about choosing one platform — it's about integration. By 2027, most Irish enterprises will use unified, cloud-based communications that blend SIP connectivity for resilience, hosted PBX features for flexibility, and Teams or UC platforms for collaboration.
Conclusion
The right voice solution depends on your business structure, infrastructure and strategic goals. Whether you're extending an existing PBX, migrating fully to the cloud or integrating Microsoft Teams, the foundation is always the same: reliable connectivity, secure architecture and expert design. Choosing the right partner is what turns that technology into competitive advantage.