Know which numbers can receive a text — and how you know
Line type from the carrier the block is allocated to — Mobile, Landline, VoIP or Paging, each verdict carrying its evidence — with live HLR as the authoritative check for the numbers that matter.
Texting a landline is a silent failure: the message dies, the campaign metrics rot, and on some routes you still paid for the attempt. Filtering by line type first is the cheapest fix in messaging.
The catch is that the US numbering plan does not record line type, so every vendor answering this question is inferring it. The difference is whether they tell you what the answer rests on. Ours says it: the carrier the block is allocated to — a Verizon Wireless block is mobile the way a Pacific Bell block is a landline. Measured on the full NANPA file, 87% of prefixes classify; the rest say unknown instead of guessing.
The endpoints, and what each costs
POST /api/lookup-phone
{ "phone": "+19072015550", "country": "US" }rows: [
{ "label": "Line type", "value": "Mobile (allocation)" },
{ "label": "Line type basis", "value": "Block allocated to a wireless carrier
(CELLCO PARTNERSHIP DBA VERIZON WIRELESS)" },
{ "label": "Carrier note", "value": "ported numbers need a live HLR lookup" }
]The verdict and its evidence travel together. A bare 'mobile' from any vendor is this same allocation data with the basis stripped off.
The part a use-case page usually skips
Allocation cannot see porting
A number moved from Verizon Wireless to a landline carrier keeps its digits. Block allocation is right about the overwhelming majority and silent about the ported minority — which is why the response names live HLR as the authoritative check instead of pretending the gap away.
VoIP numbers vary
Some VoIP services receive SMS, most do not, and the allocation cannot tell you which. We class the block as VoIP and leave the send decision to you.
Reachability is not consent
A number that can receive your text is not a number you are allowed to text. Consent rules for SMS marketing are stricter than for calls — pair this with your own consent records and the DNC product's scrub log.
Why do you say 87% and not 100%?
Because 11% of prefixes are pooled blocks shared by several carriers or held by operators whose class we have not verified, and the honest answer there is unknown. Vendors reporting 100% coverage are answering those prefixes anyway — from the same data we declined to guess on.
When is HLR worth the extra cost?
When a wrong answer is expensive: verifying the destination before an OTP flow, checking high-value contacts, or auditing the ported slice of a list. HLR is a live network query we buy per call and price as a visible pass-through, not something folded invisibly into a cheap answer.