CLI (Calling Line Identification)

CLI (Calling Line Identification) in voice termination refers to whether the caller’s original phone number is preserved and accurately delivered to the called party as calls transit carrier networks. A route with full CLI pass-through displays the genuine originating number on the recipient’s phone. Routes without CLI pass-through may display a substitute number, a generic carrier number, or no number at all. For businesses making outbound calls, CLI quality directly impacts answer rates — calls displaying a recognisable local number are significantly more likely to be answered than calls showing unknown or international numbers.

Contact centres live and die by answer rates. When an agent dials a customer and the call displays as ‘Unknown’ or an unrecognised international number, that call is far more likely to go unanswered or be rejected. Studies consistently show that local or familiar numbers achieve significantly higher answer rates than anonymous calls. Using a carrier with certified CLI pass-through means your outbound calls display the correct number, protecting answer rates and ensuring your STIR/SHAKEN attestation (and CNAM data where applicable) is transmitted accurately.

CLI routes guarantee that the originating caller’s number is passed through intact to the destination. Non-CLI routes — sometimes called ‘anonymous’ routes — either strip the calling number or replace it with a carrier-assigned number. CLI routes are more expensive because they require deeper carrier interconnections and compliance with destination network requirements. Non-CLI routes are used for price-sensitive traffic where answer rate optimisation is less critical. For regulated industries or contact centres, CLI routes are typically required.

IDT Express Platinum CLI certification is a quality designation for voice termination routes that guarantees full caller ID pass-through, high answer-seizure ratios (typically above 65%), low post-dial delay (under 3 seconds), and no number substitution. Platinum routes use direct interconnections with destination networks rather than intermediary carriers, reducing both the risk of CLI manipulation and the latency introduced by multi-hop routing. For contact centres and enterprises where call quality and answer rates are commercially critical, Platinum routes provide the highest available service level.