In order to make an outbound call from your SIP/Soft phone you need to follow the below steps.
Ensure your Soft phone is Configured properly
You may have a look at this tutorial on how to configure your Soft phone.
Include a callback Url with a Dial action.
This is to direct the call to the number you are dialing (here's an example in PHP)
$sessionId = $_POST['sessionId'];
// Check to see whether this call is active
$isActive = $_POST['isActive'];
if ($isActive == 1) {
// Forward by dialing customer service numbers and record the conversation
$callerNumber = $_POST['callerNumber'];
// Compose the response
$response = '<?xml version="1.0" encoding="UTF-8"?>';
$response .= '<Response>';
$response .= '<Dial record="true" sequential="true" phoneNumbers="'.$callerNumber.'"/>';
$response .= '</Response>';
Now just dial the number from your soft phone.
If this does not work you may check out this article on why was my call aborted.
You may also send an email to voice@africastalking.com