Landlines, Mobiles, and Whether SMS Can Arrive
A verified number is not the same as a textable number
What It Is
Phone verification answers two separate questions.
The first is whether the number exists at all, and in what canonical international form. The second — for numbers in the United States and Canada — is whether the number belongs to a mobile or to a landline. That answer comes from a carrier, and it is the only reliable source for it: the numbering plan those two countries share does not reserve separate ranges for mobiles, so the number itself cannot tell you.
Outside the United States and Canada, most countries do separate the ranges, and the line type comes from the number's own structure.
A verified phone number therefore shows a line type badge on Manage Contacts — mobile, landline or voip — next to its green seal.
Why It Matters
An SMS to a landline cannot arrive. It is not delayed or filtered; the medium does not carry it. But it is charged for, and from the sender's side it looks exactly like a contact who never replies.
So a database that cannot tell the two apart quietly pays to send messages into nothing, and then reads the silence as disinterest. On one account, the first phone verification run found 8 landlines among the contacts it checked, and every one of them was still enrolled for SMS.
The opposite mistake is just as costly in the other direction. Suppressing SMS to a contact who could have received it loses the channel silently, so Zyntro only suppresses when a carrier actually said landline — never on a guess.
How It Works
Three answers, not two
Whether SMS can arrive has three possible values, and the third one is load-bearing:
- Yes — a carrier identified the number as a mobile, or the numbering plan did.
- No — a carrier identified it as a landline.
- Unknown — nobody could tell.
Unknown is treated as unknown. Nothing is suppressed on it, because an unproven suspicion is not grounds for removing a channel. Numbers that carry an internet-telephony signal land here deliberately: some of those services do accept SMS, so they are left alone rather than assumed dead.
What happens automatically
When a verification job finds that a number is a landline, Zyntro sets that contact's SMS opt-out. The effect is immediate: single SMS sends refuse the contact, and SMS broadcasts exclude them.
Three things it deliberately does not do:
- It does not mark the contact do-not-call. A landline answers calls perfectly well and is often the best number you have left.
- It does not turn off automated engagement. Being unable to text someone is not a reason to stop engaging them.
- It never clears an existing opt-out. If a contact asked not to be texted, that decision survives, and a number that later moves to a mobile network is not silently re-enrolled.
Undoing it
The suppression is a statement about the medium, not about the person, so you can reverse it. Clear the SMS opt-out on the contact's own page, or in bulk with Set Field on the contacts table.
An automatic suppression and a deliberate one remain distinguishable on the contact afterwards, so a later review can tell which is which.
Examples
A contact shows a green seal beside their phone number and a landline badge
The number is real and was confirmed. It is a landline, so this contact's SMS opt-out has been set and they will be skipped by SMS broadcasts from now on. Their calling channel is untouched — if anything, this contact is now a better call target than a text target.
A UK number comes back verified with no line type badge at all
The carrier check covers United States and Canada numbers only. For other countries, the line type comes from the number's own structure where that is meaningful, and is left blank where it is not. Nothing is suppressed on a blank.
You run a phone job and your wallet is charged for numbers that turn out to be landlines
A landline is a successful verification with a useful answer, so it is not refunded. What you bought was the knowledge that texting that contact would be wasted, which it now acts on automatically.
Info: A number's line type can change. People move numbers between carriers, and a number that was a landline two years ago can be a mobile today. Re-verifying a contact is the only way to pick that up.
