For SaaS, marketplaces and consumer apps
Check the number before you send the signup code. One lookup says whether it's a mobile, landline or VoIP line from a live carrier dip, whether a carrier deactivated it in the last 45 days, whether it's on our blacklist, and whether it can take a text. You stop paying for codes that can't arrive, and you see which signups deserve a second check.
| Number | The lookup says | Do this |
|---|---|---|
| (415) 555-0186 | Active mobile | Send the code |
| (737) 555-0142 | VoIP line | Add a step |
| (213) 555-0119 | Landline, can't take texts | Offer a voice code |
| (602) 555-0170 | Deactivated by the carrier Oct 6 | Ask for another |
| (917) 555-0133 | On our blacklist | Manual review |
Fictional 555 numbers.
About 32% of the numbers we look up are landline or VoIP. A landline comes back with action: "unsubscribe" and reason "Not a valid mobile number", so you can skip the text and offer a voice code instead.
Source: CheckThatPhone lookup data
actionreasonnanpType A code proves someone can read a text on that number right now, not who they are. dipCarrierSubType "IPES" marks a VoIP line, from a live carrier dip. Plenty of real customers use VoIP, so treat it as a reason for another step, not an automatic block.
dipCarrierSubType = IPES deactivationDate shows a carrier deactivation in the last 45 days, and reason names the carrier id and the date. Ask for a working number before you send a code.
deactivationDatereason Compare digits, not what people typed: the API strips spaces, dashes, parentheses and + and expects 10 digits, or 11 starting with 1. Do the same before you check a number against existing accounts. One-account-per-number rules stay yours.
subscriber Call the API when the person submits a phone number, before your SMS provider sends anything. Pass the signup's IP as ip to get location and time zone from the IP. If action isn't "send", don't text: offer a voice code or ask for a mobile.
Weigh VoIP, a recent deactivation and the blacklist flag alongside email, device and payment signals. Allow, add a step (another factor, a card check, a smaller trial), or send to review, with thresholds you tune on your own outcomes.
Before a referral bonus, a promo credit or a change to sign-in details, look the number up again and compare dipCarrier and dipOcn with what you stored at signup. A different carrier means the number moved since then.
None of these proves fraud on its own. They are inputs to your rules; the allow-or-block call is yours.
| If the response shows | Field | Do this |
|---|---|---|
| Can take a text | action = send | Send the code. |
| Landline | nanpType = landlinereason | Don't text. Offer a voice code or ask for a mobile. The landline SMS check (+1 credit) finds landlines that can take a text (smsEligible). |
| VoIP | dipCarrierSubType = IPES | A risk input, not a block: add a step, or hold back trial credits until another signal checks out. |
| Deactivated by the carrier recently | deactivationDatereason | Don't send the code. Ask for a working number. |
| On our internal blacklist | blackList = truereason | Send to review or block. reason reads "Blacklisted Subscriber". |
| A different carrier than at signup | dipCarrierdipOcn | The number moved carriers since signup. Add a step before a payout or a change to sign-in details. |
| Ported | dipPorted | Not a recency signal: it has no date, and it isn't a SIM-swap check. Compare carrier fields over time instead. |
| Signup location | geoStategeoSourceipResult | With an ip passed, location comes from the IP; without one, from the area code. One call returns one or the other. ipResult only says the IP was valid. |
An active landline. action is "unsubscribe" with reason "Not a valid mobile number", so a text code would never arrive: offer a voice code or ask for a mobile. No IP was passed, so location and time zone come from the area code (geoSource: "area-code").
Highlighted fields: action, reason, nanpType, dipCarrierType.
{
"success": true,
"credits_used": 1,
"data": {
"subscriber": "2135550119",
"optDate": "2026-10-09T17:22:08.415Z",
"action": "unsubscribe",
"deliverable": "false",
"reason": "Not a valid mobile number",
"nanpType": "landline",
"blackList": "false",
"dip": "success",
"dipLrn": "2135550119",
"dipPorted": "false",
"dipOcn": "9740",
"dipCarrierSubType": "RBOC",
"dipCarrier": "Pacific Bell",
"dipCarrierType": "landline",
"geoState": "CA",
"geoCity": "los angeles",
"geoCountry": "US",
"timezone": "America/Los_Angeles",
"tzOffset": 8,
"geoSource": "area-code",
"error": "false",
"doNotSms": "true"
}
}Monthly cost:
A plain lookup, no add-ons needed for these signals. Computed from the published plans. The free plan's 500 lookups a month cover testing.
IPESaction) before you pay for a codeNot legal advice.
IPES) is the closest signal, and many VoIP users are real customers.dipPorted says a number moved carriers at some point. It has no date, so it is not a recent-port or SIM-swap signal.deactivationDate: data refreshed daily, with a 1 to 7 day lag, and entries expire after 45 days. It is not a reassigned-number check.No. The code proves the person can read a text on that number right now. The lookup runs before it: it tells you whether the number can take a text at all, and whether it looks worth a closer look, so you only pay for codes that can arrive.
Usually not outright. Many real customers use VoIP lines. Treat dipCarrierSubType "IPES" as one input: add a step, hold back trial credits, or review, and measure the result on your own signups.
No. A SIM swap moves a number to a new SIM at the same carrier, a different thing from a port to a new carrier (FCC 23-95, paragraphs 5 and 6). dipPorted says the number was ported at some point, with no date. To spot a carrier change, store dipCarrier and dipOcn at signup and compare them on a fresh lookup before a sensitive action.
Not by itself. It doesn't link different numbers to one person or return owner names. It helps with the number part: compare the digits against existing accounts, and treat VoIP, recent deactivations and blacklisted numbers as inputs to your rules.
The API covers US and Canadian numbers only. It expects 10 digits, or 11 starting with 1; anything else comes back as an invalid request, with no credit charged.
Same lookup, different job. The KYC page is about account opening at fintech and lending companies. This page is about any app that sends a code at signup and wants to keep fake accounts, trial abuse and wasted texts down.
500 free lookups a month to try it on your own signups. One credit per lookup after that.