PSTN to Cloud Calling – 6 Key Considerations

PSTN to Cloud Calling – 6 Key Considerations

Written by Rob Quickenden,
Cisilion’s Chief Technology Officer 

As the telecommunications landscape continues to evolve, the Public Switched Telephone Network (PSTN) is gradually being phased out in favor of modern communication technologies. It will be completely switched off by the end of December 2025, and new PSTN lines can no longer be bought or sold.

This transition presents both opportunities and challenges for organisations that rely on traditional phone systems. The future and replacement, of course, lie in Cloud Calling. However, achieving a smooth transition requires careful thought, planning, and migration.

Moving calling into the cloud also helps extend the functionality and reach of collaboration solutions like Microsoft Teams, Zoom, and Webex, for example. This blog discusses the six key considerations for businesses in preparation for the PSTN switch-off next year and covers seven essential areas.


1. Assess Current Calling Infrastructure

To prepare for the PSTN turnoff, you should first examine your current telephony infrastructure. Find out how many PSTN lines, hardware devices, and related costs you have. Check if you have any legacy systems that depend on PSTN connectivity, such as fax machines or alarm systems that use analogue connections. This assessment will help you measure the impact and look for appropriate alternatives.

Action: Speak to your UC or voice partner – They will be able to carry this out for you and help you with costings and options.


2. Explore Different Cloud Calling Options

With traditional PSTN services becoming obsolete and being turned off, cloudbased communication solutions, such as Microsoft Teams not only offer more advantages but make lots of sense for organisations by having a single platform for meetings, chat, calling, and apps. Moving towards integrated solutions helps you save costs, scale up and down as needed, and provide a simpler unified, and easier-to-use platform with everything in one place. It also is proven to improve adoption and make communication more “frictionless” as well as providing better integration with other lines of business applications.

The same applies to organisations that are already invested in wider UC platforms such as Webex or Zoom. To find the best solution for your organisation, you need to assess your needs and goals. You may also benefit from working with a trusted technology partner who can guide you through the migration process.


3. Network Readiness Assessment

Before implementing your chosen cloud voice solution, make sure your network infrastructure can support it. Unlike traditional PSTN or dedicated “voice solutions”, putting cloud calling alongside your collaboration and productivity solutions like Teams, Zoom or Webex typically means that IP routing, VLANs, bandwidth, and QoS settings will need to change.

You’ll need to check internet bandwidth, wired and wireless networking, VLANs, VPNs, and network security. You may also need to add or implement CoS and QoS to to ensure quality of service. Your cloud provider, IT or technology partner will be able to help – so will the chosen vendor you decide to work with and many will have “tools” to help you check connectivity health.


4. Not all Cloud Calling is the Same

To transition from PSTN to a different phone system, it is essential to carefully compare the various methods of connecting your calls. When considering the inclusion of cloud calling in your collaboration suite, such as Webex, Zoom, or Microsoft Teams, multiple options are available. Whilst these vendors all provide their own native “calling plans,” which may be the simplest and most suitable choice in certain cases. It is also important to explore alternative connectivity methods, such as Direct Routing (via SBCs managed by you or your partner) or Hosted Direct Routing (a managed service).

Additionally, you may even consider utilising solutions that are not inherently integrated into your collaboration suite. Instead, these solutions involve an app that runs alongside or within the Microsoft Teams, Webex, or Zoom apps, providing calling capability.

For each of these options, it is crucial to thoroughly consider the advantages and disadvantages, such as cost, seamless communication, geographical coverage, SLAs, and level of integration with other lines of business applications like Office 365, Contact Centre, and CRM. It is highly recommended to conduct tests whenever possible to evaluate the performance of each solution.


5. Have a Solid Test and Rollout Plan

An inclusive testing and migration plan must be formulated to ensure a seamless transition to the new environment. This plan should encompass pilot testing, deployment, and migration milestones, specific timelines, and clearly defined responsibilities for each transition stage.

Prior to proceeding with a full-scale production rollout, it is strongly advised to conduct a network readiness assessment (as mentioned above) in conjunction with systems testing involving a select group of users based on a user acceptance test plan.

In order to aid employees in adapting to the new system and to facilitate their feedback, it is imperative to incorporate comprehensive training and change management activities. Regular communication with stakeholders and designated “champion groups” should be established and their expectations managed consistently throughout the transition process.


6. Security, Compliance, and Privacy

For organisations operating in regulated industries, it is imperative to carefully consider and select an alternative communication solution that aligns with regulatory and compliance requirements. Factors such as data privacy, security measures, and industry-specific regulations should be taken into account when evaluating communication solutions. Additionally, the seamless integration of features like language translation, call recording, and transcription into your existing collaboration tools should be carefully considered.

A recent development worth noting is Microsoft’s announcement regarding the inclusion of Copilot functionality in Teams Phone. However, it is crucial to involve your legal and compliance teams in order to address any potential issues and adhere to relevant standards. If necessary, consult with your vendor or partner to ensure compliance and resolve any concerns.



As the deadline for switching off the PSTN approaches, organisations can benefit from adopting a modern and integrated cloud calling platform that offers better features, more flexibility, and greater affordability and future-proofing. They can also use this opportunity to streamline and simplify their communications by choosing solutions that integrate with their wider communication and collaboration tools such as Microsoft Teams, Webex, or Zoom.

For more information on how Cisilion can make the move from PSTN to cloud calling as seamless as possible, complete the form below and our team will be in touch.