Unknown numbers campaign is created to manage all of the unregistered phone numbers or leads not belonging to any campaign. 
It is created when:
1. Dialing out an unknown/un-registered number
2. Receiving calls from unknown/un-registered number
3. Sending an SMS to unknown/un-registered number
4. Receiving SMS from unknown/un-registered number

Below is an interactive example showing you how the "Unknown numbers" is created.

Click on the "Try It" option to display other viewing options and switch to full screen for better learning experience.

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16 STEPS

1. "Unknown numbers Campaign" is created when an Unknown number or leads not belonging to any campaign is used to for Incoming and Outgoing Calls and SMS.

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2. Notice that there's only one campaign here. In this example, a call-out was made to an unregistered number. This number does not belong to any campaign.

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3. Calling

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4. Click to end the call

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5. Click Campaigns to refresh the page

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6. Notice that a new campaign has been created. Unknown numbers

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7.  Unknown numbers Campaign

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8. Unknown Phone Number

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9. Sending and receiving SMS from a non-registered phone number or unknown number will also create the "Unknown numbers" campaign.

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10. Click Quick SMS 

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11. Use a number not belonging to any campaign and send SMS

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12. Type Message text

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13. Send Message

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14. Sent SMS confirmation

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15. Click Campaigns to refresh the page

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16. Unknown numbers campaign was created.

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Here's an interactive tutorial

https://www.iorad.com/player/1782877/What-is-an--Unknown-numbers--Campaign-

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