It really all depends on your needs and your understanding of what SIP trunking is?
Several internet providers can provide sip trunking, but not all sip trunk providers can provide internet.
One of the biggest worries you will have with sip trunking is latency, and most carriers can provide that data within their QoS (Quality of Service) reports. Generally (as always) we like to see as small of an amount of packet loss in the transmissions as we can. For voice calls 1% or less packet loss would be an excellent quality call.
You will see codecs mentioned by providers, and if your using an open source VOIP server, it will support all codecs, and this should not be an issue as most carriers conform to a standard that is now well supported throughout the VOIP industry.
If you are not hosting your own solution, you obviously should be concerned with a usable control panel, as well as Call detail records interface so you can see what calls where sent/received and when.This is something you will want to track closely as the number of calls made from your system can affect billing on a monthly basis. The times calls are placed can also indicate a potential intrusion into the system as well.
Packaging can vary greatly from provider to provider as well, the number of channels supported to the cost per call. Careful investigation into pricing packages based on your specific needs of the system your running will make a big difference in your pocket book down the road. Also with VOIP, you are now utilizing E911 which will incur fees when a 911 call is placed, so you also want to be aware that even an accidental call placed can incur the fee, as well as alarm systems that may end up tied into the phone system.
Your SIP trunk may connect back to multiple servers in different locations based on the providers network, and this ensures maximum uptime for your system. It is a simply redundant system set up to make sure you are always connected, so it is a good idea to ask, how that will work based on a given package you may be looking at. After all, if your SIP trunk provider is not connected, you are not connected, so call quality and price may be great, but a provider without any type of fail over plan, will not be as reliable as the provider with a viable plan in place.
Does the provider also have a block of sequential DID numbers available for you? This may not be an issue for everyone, but if this is a part of how you choose to set the system up, it can become extremely important, and I have seen from experience that sequential DID’s can be extremely helpful to business.
If you have designed your own system, or are simply looking to have your system hosted, understanding how you plan on using that system, what the needs of your business, and employees are in regards to that system will supply more than enough information to choose a quality provider for the best price. The first step is to know your needs and how you will use the system.