First: which of the two things do you want?

Almost every problem with this comes from conflating two different operations. They have different forms, different requirements and different outcomes.

• Transfer the line to its own account at the same carrier. The number stays, the person becomes their own account holder, and nothing is ported. Verizon calls it Assume Responsibility; AT&T calls it Transfer of Billing Responsibility; T-Mobile handles it as a change of account ownership.
• Port the number out to a different carrier. The number moves to a new company, and the old line closes automatically once the port completes. This is what you want if the person is leaving for a cheaper plan.
• Cancel the line outright. The number is released and, after a grace period, recycled. Only do this if nobody wants the number — it is not reversible once the number is gone.

Option 1: transfer the line at the same carrier

This is the right path when the person wants to keep their number and stay with the carrier — an adult child taking over their own bill, or one person keeping the line after a separation. It is a two-sided process: the current account holder starts it, and the person receiving the line has to accept and pass a credit check to open their own account.

1. The account holder initiates the transfer in the carrier's app or online account, or by calling — some carriers require a phone call for multi-line accounts.
2. Settle or move any device payment agreement on that line. Most carriers will not release a line with an outstanding installment balance unless the receiving person assumes it or the balance is paid off.
3. The receiving person accepts the request, provides their own details and consents to a credit check. The request expires if they don't act, typically within a few days.
4. The new account is created with the same number, and the line disappears from the original bill on the next cycle.
5. Check what travelled with the line — insurance and device-protection add-ons, cloud storage, and any watch or tablet line paired to it usually need re-adding on the new account.

The credit check is the step that catches people. If the person taking over the line doesn't qualify on their own, the carrier may require a deposit or refuse the transfer entirely — at which point porting to a prepaid carrier, which runs no credit check, becomes the practical route instead.

Option 2: port the number to another carrier

If the person is leaving anyway, this is simpler and cheaper, and it removes the credit check from the equation. The mechanics are the standard port: the new carrier pulls the number across, and the old line closes itself.

1. Get the account number and a transfer PIN — sometimes called a port-out PIN — from the current carrier. This is separate from any voicemail PIN, has to be requested deliberately, and often expires within a few days, so request it shortly before switching.
2. Confirm the account holder's authority: on most carriers only the account owner or an authorised user can request the PIN, which means this step needs cooperation if the split is not amicable.
3. Sign up with the new carrier and choose to keep the existing number, entering the account number and PIN.
4. Leave the old line alone until the port finishes — usually minutes on eSIM, up to a couple of days on stubborn accounts.
5. Pay off any device balance. Porting out does not erase an installment agreement; the remaining balance typically accelerates onto the final bill of whoever holds the account.

What removing a line does to the rest of your bill

This is the part people don't find out until the next statement, and on postpaid accounts it can be expensive.

• Multi-line discounts recalculate. Carrier pricing is tiered by line count, so dropping from four lines to three can raise the per-line rate on every remaining line — occasionally enough that the total bill barely falls.
• Promotional bill credits can stop. Device promotions are usually paid as 24 or 36 monthly credits conditional on the line staying active on a qualifying plan. Remove the line and the remaining credits generally end, leaving the unpaid device balance owed.
• Bundled perks may drop below their threshold. Streaming subscriptions and travel benefits attached to certain plans sometimes require a minimum number of lines.
• Autopay and paperless discounts stay, but they are per-line — so the saving shrinks with the line count.

If the split isn't amicable

The account holder controls the account. They can request transfer PINs, authorise removals and see usage; a non-owner on the plan generally cannot do any of those things, and carriers will not override that over the phone. If you are the non-owner and need out, the clean route is to port your number to a new carrier — which needs the account number and PIN, so it still needs cooperation — or, failing that, to accept a new number on a prepaid plan and keep the old one only long enough to tell people.

If you are the account holder and need someone off, you can remove the line without their consent, but you cannot force them to take it over. The outcomes available to you are transfer, if they accept, or cancellation, which loses the number. There is no third option, and carriers will not adjudicate the dispute.

Where the leaving line should go

Most people removed from a family plan are surprised by what a single line costs on its own, because carrier pricing hides the solo rate behind multi-line discounts. A line that appeared to cost $30 inside a four-line plan is frequently $65–$90 as a standalone postpaid line.

That is the moment to leave postpaid entirely. Visible is $25 a month all-in on Verizon's network, US Mobile's Unlimited Premium is $32.50 with a choice of all three networks, and neither runs a credit check — which also solves the transfer problem above.