Official Trixbox site.
Login to Trixbox Web admin center and switch to "Admin mode" (user maint).
For sending calls through Diamondcard you'll need to configure a Trunk.
From menu choose:
Setup->Trunks->Add SIP Trunk
type=peer username=Your_AccountID fromuser=Your_AccountID secret=Your_PIN_code host=sip.diamondcard.us disallow=all allow=gsm,ulaw insecure=invite context=from-diamondcard
If you are planning to use Diamondcard personal numbers (DIDs) you should also configure:
make it empty
To make outgoing calls you need to define outbound route. It'll associate dial prefix with certain trunk. In this example we'll use prefix 011 and tie it with "diamondcard" SIP trunk. It means when your PBX extension will dial any number started with 011 it'll be sent though Diamondcard trunk.
E.g. if extension dials 011442088461122 PBX will send call to 442088461122 (United Kingdom phone number) via Diamondcard.
You may use other prefixes too. Note that number sent to Diamondcard should be in international format. "|" symbol should be used to cut dial prefix.
To add outbound route choose from menu:
Setup->Outbound Routes->Add Route
You'll need to setup at least one extension which will be making calls. Extension configuration depends from VOIP equipment which your are going to use with PBX.
Dialed numbers which match "Outbound routes" prefixes will be sent through configured trunk.