You are responsible for all charges on your account until the new customer completes the Change of Responsibility or COR, --the account balance will not transfer to the new customer.
The new customer may need to run credit and pay a deposit.
If the Change of Responsibility drops your account to below the line amount for your rate plan, you will need to contact Customer Care to change your rate plan to a different plan once the Change of Responsibility is completed to avoid additional bills at the cost of the family rate plan.
You can keep the Magenta Complete plan if your account still meets the terms. Only Coaches and above have proper permissions to make the change. See Magenta Complete plans for more information
If you have no active lines after the Change of Responsibility completes, the account will be cancelled, and you will no longer have access to previous bills and call details on My T-Mobile. The Billing Responsible Party must remember their PIN/Passcode to verify their cancelled account. Update PIN/Passcode in customer requests.

The COR is good for 30 days.
Final payments need to be made by speaking with Customer Care, mailing it with the payment remittance slip found on your billing statement, or by visiting a Retail location.
Any future payments made via our automated system reached when calling Customer Service will be applied to the account of the party who has taken responsibility for the number(s).
Your voicemail box may be deleted and all old messages may be lost, so make sure to save voicemails you want to keep.
Please complete any needed equipment returns before transferring account responsibility. Once the Change of Responsibility is complete, devices can't be returned, however, exchanges for defective equipment can still be performed by the new subscriber.