Before you text a number from years ago, check who has it now

Here is a fictional case, used throughout this article. Dana has just seen that her old colleague Theo Lindqvist has a new job, and wants to congratulate him. The only number she has is (415) 555-0142. Their last conversation there was in June 2022.

Before she types anything, Dana should treat that number as unconfirmed. In the US, a disconnected residential number can be given to someone else after 45 days, and nothing in the phone network tells the people who saved it. Messaging apps pass on a change only in some cases, mostly when the person chooses to. The rules and apps described here are as documented for US numbers; other countries set their own reuse periods. The safe order is: look for a channel confirmed more recently; if the old number is all she has, send one short message that a stranger could read without harm; then change the contact card so the history survives without the stranger.

How fast a number can change hands

In its 2018 order creating a national database of disconnected numbers, the Federal Communications Commission estimated that "approximately 35 million numbers are disconnected and made available for reassignment to new consumers each year." The estimate averages numbering-administrator reports for 2013 to 2016. The FCC noted that at least one party questioned it and said it had received no other credible estimate. [1] Treat it as the scale of the practice then, not a current count. No source measures how often a personal contact's number goes stale.

The same order observed that someone who gives up a number "might not update all parties who have called in the past." It also recorded a commenter's assertion that some of the largest wireless carriers reassigned numbers "in as few as two days." [1] Federal rules now set a minimum: numbers previously assigned to residential customers are held for "no less than 45 days and no more than 90 days," and business numbers for 45 to 365 days. [2] The FCC chose 45 days so each month's disconnections would reach the database before reuse, with a two-week buffer, and noted that callers might hear an intercept message meanwhile. [1]

Microsoft's account help says mobile carriers "can reuse phone numbers after 30-days." [3] That page is written for every country; for US numbers, the rule above sets 45 days.

Stale numbers keep receiving messages. In a 2021 Princeton study, researchers obtained 200 recycled numbers at two major US carriers, chosen because each was still linked to an online account, and monitored each for one week between November 2020 and January 2021. Nineteen received security- or privacy-sensitive calls or texts meant for a previous owner. [4] Those came from services and other senders, not specifically friends, but the route is the same one Dana's congratulations would take.

The official database is built for businesses

The Reassigned Numbers Database answers one question: has this number been permanently disconnected since a date you supply? The reply is "yes," "no" or "no data," and the caller never sees who holds the number now. [5] It exists so that businesses calling or texting under the Telephone Consumer Protection Act can check first. It is "a pre-paid, subscription-based service for Callers and Caller Agents," and registration requires an authorizer "from the same company." [6] The smallest listed plan is 1,000 queries over one month for $8. [7] It is not designed as a personal lookup.

One idea is worth borrowing. The database asks for a "date of consent," which may be "the date when you last spoke to the consumer at that number." [6] For a personal contact, it is the most useful fact you can record about a number.

What each system tells you when someone changes number

[1] [2] [8] [9] [10] [11] [12] [13]

"Describes no notice" means we read the page and found no statement either way. Every signal in the table depends on the other person using a feature, choosing you, or going quiet long enough for an account to be deleted. A missing warning tells you nothing.

iMessage deserves a note of its own. Apple tells people who moved to a non-Apple phone and stopped getting texts that they "might need to deregister iMessage," so an old registration can outlast the switch. Even after deregistration, some Apple devices may take "a few hours" to notice. [12] A message turning from iMessage to SMS can mean a new phone as easily as a new owner, and a message that stays iMessage does not prove your friend still holds the number.

Decide before you send

Treat the number as unconfirmed if any of these apply:

1. Your last two-way exchange at that number is more than about a year old. This threshold is our editorial choice, not a published rule; the legal minimum before reuse is 45 days.
2. You have seen a newer number or channel elsewhere: an email signature, a mutual friend, a group chat.
3. Their WhatsApp profile was removed or their photo disappeared. This is a weak signal.
4. Your last message went unanswered, or someone unexpected replied.

Until the person confirms who they are, leave out health, money, family or relationship news, addresses, photos, other people's names, links to shared documents, and anything you would mind a stranger reading. Leave out their full name as well.

A first message that works for either reader (fictional):

Hi, this is Dana, from the Harbor Street office years ago. I'm trying to reach an old colleague and this is the number I have. If that isn't you, sorry to bother you. A quick "wrong number" would help me update my contacts.

Wait for them to identify themselves. "Yes, it's Theo!" is confirmation. "Who's this?" is not. If a stranger answers, thank them and stop; don't ask them to pass anything on.

Keep the history, lose the stranger

In the fictional case, Dana first emails the address in Theo's 2024 conference bio. With no reply after a week, she sends the neutral message, and the answer is "Wrong number, sorry." At no point has the new holder learned Theo's name or any news about him.

Once the reply confirms a stranger, Dana removes (415) 555-0142 from the phone field on Theo's card. Our inference, not documented behavior: while the old number stays there, a phone that matches incoming messages by number may keep labelling the stranger's texts with Theo's name. She keeps the history in the card's note instead:

Old mobile (415) 555-0142: last confirmed June 2022. Reached someone else, September 2026.

When a mutual friend later passes on Theo's new number, (415) 555-0187, she adds it with the date she confirmed it and sends her congratulations there. Writing the date down matters because you will not reliably remember it; conversation studies find that details left unwritten fade quickly, as our reading of the memory research explains.

This is the mirror image of the duplicate-card problem. There, two cards may describe one person; here, one number has belonged to two people. If the hard part is deciding to write to an old friend at all, a separate piece looks at why those messages stall.

Kluro uses names and contact details to recognize people across your connected history. It does not detect reassigned numbers. When two records do not belong together, you can keep them separate, and a generated suggestion does not override that choice.