How to call someone from a different number

Question

I’m curious about the concept of spoofing phone numbers, where a call appears to originate from a different number. How is this technically achieved, and are there legitimate or ethical use cases for it?

Answer 1

I'll break down the technical aspects of calling from a different number, also known as "caller ID spoofing," and discuss both legitimate and illegitimate use cases.

Technical Achievement

Caller ID spoofing involves manipulating the Caller ID information, which is transmitted as part of the call setup process in the Signaling System No. 7 (SS7) protocol for landlines or the Session Initiation Protocol (SIP) for Voice over Internet Protocol (VoIP) calls. Here's a simplified overview of how it's technically achieved:

VoIP or Specialized Services

To spoof a number, you typically need to use a Voice over Internet Protocol (VoIP) service or a specialized calling platform that allows for custom Caller ID settings. Some VoIP providers, online calling services, or apps offer this feature, often for an additional fee.

Number Provisioning

The service or platform must have access to a pool of phone numbers or the ability to use a provided number (yours or a spoofed one). Legitimate services usually require verification of the number you wish to display to prevent abuse.

Call Setup Modification

When a call is initiated, the service modifies the call setup data to include the desired Caller ID (the spoofed number) instead of the actual originating number. For VoIP, this involves altering the SIP headers. For traditional landline calls, it would involve manipulating SS7 signals, which is more complex and typically not done by end-users.