How do we set our business telephone number as the number to display as the calling number in a voice message?
If you are using the JobSubmit API to inject your job, you can specify the ANI (aka calling number) that you wish to use as part of the VoiceOptions element:
<VoiceOptions>
<ANI>your_business_number</ANI>
</VoiceOptions>
If you will always use the same value for all of your jobs, then that can be set in your profile on the system side so you don't need to include it with each one of your requests.