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Choosing a SIP Trunk provider: What to look for?

Choosing a SIP Trunk Providerwhat to look for

When evaluating SIP providers, it’s easy to get sucked in by technical detail. Outside of the technology itself, there are some key criteria that you should use to narrow down your shortlist. Here are the most important factors to look out for when selecting a provider of SIP trunking.

Network readiness

Will your SIP provider ensure your network is ready before implementation? Make sure your selected provider has the technical capacity to support your SIP installation, but also that they are experienced in the network elements required to operate SIP trunks too.

For your SIP trunks to work first time, and perform as they should, your network needs to be ready to accept the new SIP traffic. Failure to ready the network for SIP can lead to degraded performance.

Can they look after the network and the SIP?

Whilst not a pre-requisite, it is extremely useful if the SIP provider can look after your network too. In order to gauge deeper insights and keep on top of network performance, having everything in one place is a great benefit.

With SIP, security and quality is reliant on the network. With a good network setup, SIP will operate just fine. But, with the same provider looking after both components, security and quality can be guaranteed end to end.


Once you’ve ensured that your PBX is SIP-compatible, it is important to understand whether your PBX is interoperable with your SIP provider.

Dependent on the SIP platform used by your selected provider, certain PBXs may not be compatible. Make sure you check the SIP interoperability list to ensure your PBX is interoperable. If your PBX is not listed as compatible, you may need to invest some time ahead of implementation to conduct interoperability testing.

This is also the best opportunity to check that your non-PBX devices can be supported via SIP. Legacy devices such as fax, alarms and credit card machines may have previously been connected to your PBX via ISDN or PSTN lines. Ensure your new SIP provider can facilitate the use of these services over the new connection. You may require additional equipment such as analogue adapters or a media gateway.


When you know that your PBX is compatible, you need to make sure the SIP trunks will be supported in all your locations. If you are a UK-based business with one or two offices, you will be adequately supported by most SIP providers.

However, if you have complex multinational requirements, like overseas offices that need to talk to each other, the shortlist must be reduced further. Some providers specialise in international deployments, others offer it but may have little experience in this area. Make sure you fully understand your SIP provider’s capability and experience when deploying SIP over multiple sites, and across multiple countries.

User acceptance testing

Other than interoperability testing (if required), the other testing you should expect your SIP provider to conduct is extensive user acceptance testing. Providers that allow SIP trunking to go live without any form of testing should be avoided.

To ensure your SIP service is fit for purpose at the point of go live, testing should run through common calling scenarios as well as things like emergency services that are crucial but not necessarily top of everyone’s agenda to test.


Reviewing financial status is important when looking for a SIP provider. Whilst this is a key requirement for everybody, the SIP market is all about the number of subscribers. Review the number of users, customers and revenue as well as net worth.

It’s more important to discover which SIP provider matches your own business. If you have less than 50 employees, you can’t expect a dedicated approach from giant telecoms corporations. There are vendors specialising in SIP for small and medium businesses which will be a better fit. It is also worth noting current customer bases to ensure your VoIP provider can relate to your industry.

You should also ensure the SIP offering is competitive in the market. Whilst SIP pricing is similar across the board, rates do need to be competitive to win customers. Do be wary of costs being cut due to the exception of things like user acceptance testing or not being able to log a fault if SIP dips below acceptable quality.

Post install experience

Once your SIP service is live, it is important to be aware of the experience you will receive from the post-implementation teams. Traditional telecoms companies assigned account managers that were sales-focused. In the modern era, where customer experience is key, you should look for a provider that issues a customer success manager or similar.

This type of role is designed with you, the customer, in mind. Their role should be to ensure that your service and products are always performing to your expectations. This is a welcomed change to an account manager who is targeted on selling more products into your account – regardless of service levels.

When things go wrong

Another post-install factor to consider is support. There are some key areas to look out for when evaluating your support.

Firstly, do the support hours mirror your operating hours? It’s no good signing up to a SIP provider that only operates Monday to Friday, if you operate over the weekend. If your service fails on a Saturday morning, leaving a fault unresolved until Monday could be detrimental to business.

Secondly, look at the processes and procedures that your SIP provider abides by. Do they operate by recognised industry standard methodologies? Is their fault logging procedure and escalation process documented?

Failure to communicate how a fault will be dealt with could prove costly when you need to resolve a problem in real time.

Setting expectations is key when choosing a SIP trunk provider. As much as a provider can communicate to the wide world, the onus is often on the IT manager or buyer to make sure everything is in order before ordering SIP trunks. This guide should be used as a checklist to walk you through each consideration when selecting a SIP provider. At any point, if you require assistance with validating your SIP provider, reach out to one of our SIP experts for help.

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