Line Type Detection
Classifying a phone number as mobile, landline, or VoIP by querying carrier databases — critical for distinguishing dialable real numbers from defunct VoIP forwards.
Line type detection (also called number lookup or carrier lookup) takes a US phone number and returns the carrier's classification: mobile, landline, fixed-VoIP, or non-fixed-VoIP. The data comes from real-time queries against telecom carrier records, routed through specialist carrier-lookup APIs that license access to the underlying number-portability databases.
Why it matters for prospecting: roughly 30% of any local-business phone list is unreachable when dialed cold. Many are non-fixed-VoIP numbers from defunct registrars, abandoned business lines, or fax-only landlines. Without line-type filtering, an agency's outbound caller spends the first hour of every dial session on dead numbers.
For SMS-based outreach, line type is even more critical — sending a marketing SMS to a landline incurs telecom charges and surfaces no engagement. Filtering to mobile-only before the first send saves both reach and money.
Related terms
- Mobile vs Landline vs VoIPThe three primary phone-line classifications — mobile (cellular), landline (POTS or modern equivalent), VoIP (internet-routed) — each with different reachability and cost implications for outbound agency calls.
- DNC ScrubbingPre-checking phone numbers against federal and state Do-Not-Call lists before outbound dialing to avoid TCPA violations and known-litigator traps.
- TCPA ComplianceAdhering to the Telephone Consumer Protection Act — the federal law governing outbound calls and texts in the US, enforcing consent rules, calling-time windows, and DNC respect.
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