In a marketing campaign without tracking, it's impossible to determine which campaigns are successful and which ones aren't. Campaign tracking is essential for any advertising or marketing campaign. The challenge lies in tracking offline advertising such as print ads, which requires unique promotional URLs or coupon codes. Nexmo virtual numbers can help solve this problem by allowing users to dial a unique number that can be tracked within existing business intelligence tools. To track inbound telephone callers, the system uses the Nexmo API to request a call control object (NCCO) from the URL provided, which contains actions such as streaming an mp3 file or recording and connecting the call to an agent. The NCCO also includes the number called in E.164 international format, allowing for accurate tracking of the campaign, caller, and call information. The system uses Mixpanel to store and analyze this data, including information about the caller's name, country, and network type. By using a unique identifier such as the telephone number or campaign name, the system can track subsequent events and segment data to evaluate campaign performance.