ANI (Automatic Number Identification) is the calling number the telephone network uses to know which line to bill, and which identity to pass to certain terminating features. It originated as a Bell System mechanism for automated billing of long-distance, and it became part of equal-access Feature Group D: the interexchange carrier receives ANI digits from the local switch so it can rate the call.
ANI is a network identity. Caller ID (Calling Party Number, CPN) is a presentation identity. They often contain the same digits. They are allowed to differ. A PBX or SIP trunk may present a main DID as Caller ID while ANI still reflects a trunk or billing number. Spoofing tools rewrite CPN more often than they rewrite true ANI, which is why some enterprises and emergency systems treat ANI as the more reliable of the two, without treating either as cryptographic proof. For authentication of IP-originated calls, see STIR/SHAKEN.
*67 hides Caller ID, not ANI
Calling Number Delivery Blocking (*67 in the NANP) sets the presentation indicator on Caller ID to restricted. The called party’s phone typically shows “Blocked” or “Private.” The originating network still has a billing identity. Terminating carriers, operator services, and E911 systems still receive ANI (or the equivalent callback number). Privacy from a consumer handset is not privacy from the network.
ANI vs Caller ID vs Charge Number
| Field | Purpose | Visible to the callee? | Affected by *67? |
|---|---|---|---|
| ANI | Billing and network identification of the calling line | Not as a consumer display. Available to carriers, some IVRs, and emergency routing | No. ANI remains on the billing path. |
| Caller ID / CPN | Number presented to the called party | Yes, unless presentation is restricted | Yes. Presentation is restricted; the phone does not show the number. |
| Charge Number (ISUP / SIP) | The number to bill when it differs from CPN (common on PBX and VoIP trunks) | No | No. It is a billing parameter, not a display parameter. |
| CNAM | Optional 15-character name dip on the presented number | Sometimes, if the terminator dips | If CID is blocked, there is usually no number to dip. |
Emergency services and terminating applications
E911 needs a callback number and a location. Historically that callback number is ANI. VoIP E911 replaces the old analog ANI with a provisioned emergency location and a callback DID, but the principle is the same: emergency routing must not depend on a caller-set presentation number.
Some What is IVR? and call-center platforms still speak of “ANI dips” meaning they read the network calling number (often the SIP P-Asserted-Identity or a telco ANI parameter) to pop a customer record. That is not CNAM. It is also not a substitute for consent or for STIR/SHAKEN attestation when the question is “was this number spoofed?” See Caller ID spoofing.