Security
This is one of the most important aspects of your SIP Trunk decision process. SIP Trunks are exposed to the Internet, so a well-secured network and an anti-fraud and monitoring system should be in place by your SIP Trunk Provider.
Who is the upstream Carrier?
In Australia there are only a handful of upstream carriers, like AAPT, Telstra and Optus. Most SIP Trunk Providers will resell/rebrand from an upstream carrier or potentially from a wholesaler. Find a provider who has control over their service and network to reduce call quality issues and limit downtime.
Competitive Pricing
Pricing will vary widely between vendors; some will overcharge for SIP Trunks but the cheaper ones will over subscribe their services. Look for competitive rates, but ensure that you are getting a business-grade SIP Trunk service. Be cost-conscious, but expect to pay a bit more for business-class service.
Number Porting
Can the SIP Trunk provider port your phone numbers? Ensure that you choose a provider who can port all your existing numbers – not all providers are able to do this for all regions throughout Australia. It’s a lot of hassle if you find out they can’t later on.