Clerksroom is a national chambers of barristers and mediators providing advocacy, advice and mediation at all Courts and Tribunals in England and Wales. Clerksroom was launched in 2001 with the objective of providing proactive, client-focused legal services. It is an environment and a culture where barristers and clerks can work together in a way that guarantees the consistent delivery of a high quality and cost-effective legal service.

Driver for change 

During the first Covid-19 lockdown, when most organisations switched to remote working, Clerksroom Barristers Chambers (Clerksroom) decided that they wanted to use Microsoft Teams for voice calls too. They were heavily invested in Microsoft and wanted more integration, control and centralisation from their phone system, having realised that their legacy VoIP system lacked features and functionality. They needed to find a partner with an excellent reputation and strong pedigree for deploying business voice solutions, which is why they turned to Blackstar Solutions. 


  • Microsoft 365 Business Voice 
  • Microsoft Teams Direct Routing Service 
  • SIP Trunk Call Manager 


  • simple to use, centralised phone system with click to dial functionality 
  • Call control and phone calling capabilities, allowing you to make and receive external calls without the requirement for a desk phone 
  • Replacing a business phone system with a secure, cloud-managed service 
  • Retain existing phone numbers 
  • Employees can work from anywhere using collaborative tools in addition to voice calls, such as chat, screen share, video calls and meet 
  • A single application for all collaboration and communication requirements  
  • Improved staff productivity and enhanced user experience 

Deciding on the strategy

In March 2020, employees from organisations across the country had to start working from home almost overnight. The same was true for Clerksroom. They were not entirely satisfied with their legacy VoIP system, so it made sense to consider a new communications strategy, especially with so many remote workers. Clerksroom had used the Microsoft suite for some time, including Office 365 for emails and Microsoft Teams as a unified communication and collaboration platform, consisting of instant messaging, file sharing, video meetings and file storage.  

The logical step was to use the business phone system too: Microsoft 365 Business Voice. It enables phone calling capabilities in the Office 365 cloud, allowing you to make and receive external calls without the requirement for a desk phone. Employees have the flexibility and choice to use their mobile devices, a headset with a laptop or PC, or one of many IP phones that integrate with Microsoft Teams. 

Clerksroom approached Blackstar Solutions (Blackstar) to deploy Microsoft 365 Business Voice because of their reputation as an experienced business voice solutions provider, with proven technical abilities. 

Microsoft 365 Business Voice has to connect to the public telephony network, either using Calling Plans or via Direct Routing Services. Calling Plans are provided on a per-user-per-month basis and consist of a phone number for inbound calls and a bundle of minutes for outbound calls; whilst they are simple to deploy, the monthly license cost is high.  

Direct Routing is more flexible as bundles of minutes can be tailored to the needs of an organisation so that they only pay for the minutes they use, and the monthly license cost is significantly lower. Clerksroom put their trust in Blackstar’s advice and decided that Direct Routing was the most flexible, accessible and cost-effective option for their needs. 

The solution  

Blackstar deployed Direct Routing into a third-party hosting provider’s data centre that Clerksroom was already using, highlighting Blackstar’s flexibility and experience in multi-vendor deployments. Blackstar also ported the existing phone numbers from the legacy VoIP system and onto Microsoft Teams. The connection between the SIP trunk and the Microsoft 365 Business Voice is achieved using a virtual Session Border Controller (SBC), which allows Clerksroom to make external calls using Teams. 

Blackstar also suggested installing SIP Trunk Call Manager for added functionality. It not only gives Clerksroom business continuity but it also means that they can manage all their phone numbers and all aspects of their inbound calls, such as setting up queues and redirecting callsBlackstar set up the failover system for external numbers so that Clerksroom would have ‘business as usual’ resilience if the internet or servers went down. 

They explored various endpoints and devices and decided on a combination of Teams desk phones and headsets for added flexibility. 

Deployment and number porting 

Blackstar installed the new Teams telephony solution in December 2020 and it went live in January 2021.  The transition was exceptionally smooth: it was all pre-programmed and ready for a daytime cut over to port the numbers, which had to be done during working hours.  

It was important to minimise the downtime, which Blackstar succeeded in doing. Their engineers had completed all the scripting and had set up report groups in advance, also making sure they were on hand on the day for any potential issues 

Microsoft 365 Business Voice has been deployed on a rental model on a cost per user per month with zero Capex upfront.  

The final part of the new system deployment was user and admin training, also carried out by Blackstar’s in-house trainerBlackstar manages any ongoing support issues for Clerksroom and as yet, there have been none. 

Excellent results 

One of the main benefits of migrating their voice services to Teams is that Clerksroom can also integrate their purpose-built ‘Case Management System’ (CMS) for critical ops with Microsoft. They already integrate Office 365 for emails with the CMS and now they can also link the telephony solution. All phone numbers are incorporated into the CMS with hyperlinks so it’s remarkably simple and easy to use. It saves the clerks a lot of time as they no longer have to find phone numbers – they can just click and go.   

Elliot Mace, Sales Director at Blackstar Solutions, said, 

Clerksroom approached us with a broad range of requirements: some employees preferred desk phones whilst others favoured the soft phone approach. We listened to their needs then applied our understanding of complex voice scenarios to fulfil the demands of their diverse demographics. We enabled them to gain the flexibility and control they were after, customising the Microsoft 365 Business Voice solution to meet their specific requirements.   

Toby Ward, Business Services Manager of Clerksroom, commented: 

“The number porting was seamless and could not have gone any better. Clerksroom hatried to port the numbers to another provider about a year ago and had struggled with it so I was expecting issues, however I was pleasantly surprised with how smoothly it went with BlackstarMicrosoft 365 Business Voice is working well and is very user-friendly. This new business telephony system has improved the user experience and has really helped to simplify our IT infrastructure. 

Future plans  

Clerksroom is considering linking the CMS with Microsoft 365 Business Voice in reverse so that the clerks will be able to see who is calling, displaying their name and number via Teams.  

Another option being considered is to offer Teams phones to the (almost 200) barristers too, enabling them to use the app on their mobiles or PCs. They currently use their personal mobiles for calls so it would give them more privacy and enable them to separate work from home life.  

Whatever they decide to do, Clerksroom knows that Blackstar is always on hand for sound telephony advice. 

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