I’ve been using CallCentric as one of my SIP trunk and DID providers for several months now and it has worked really well. If you use FreePBX (or one of the prebuilt distributions that use it such as Trixbox, Elastix or PBX-in-a-flash) and use this link to sign up for a free CallCentric account I will configure your trunk in FreePBX for free.
Please use the contact form here if you would like to take up this offer.
I’ve got a few DDI numbers from CallCentric all around the world (UK, US, Australia) and couldn’t figure our how to setup an ‘Inbound Route’ in FreePBX that used the number that had been dialled to route the call.
It turns out that you need to extract the number from the ‘SIP header’ information and there’s no setting in FreePBX to do this so it means hacking at the Asterisk config files just a little.