You can assign phone numbers to traffic sources in CRM > Analytics > Sales Intelligence > Call tracking.
You can add a number manually by clicking the Add number button.
Not all telephony providers and phone numbers support call tracking, so you need to make sure that the added number supports this feature.
How it works
Click any added number and you'll get to the number check page.
You can check the number manually or you can wait for incoming calls from your clients (in this case the number check is performed automatically).
To check the number manually, enter the phone number you'll call from to the corresponding field.
Click the Start check button and make a call from the specified number to the number you want to check.
Wait the first rings and hang up. If the number supports call tracking, you'll see the message:
Also, successfully checked numbers will be marked with a green dot: