Can I swap installments to a different line?

No, swapping installment plans is not possible. If you cancel the line not being used, you will be billed the remainder owed on that installment.

Hello, @vron87! We understand that you'd like to make some rearrangements to the lines that are currently on your plan. You've come to the right place to address your concerns!

First, we'd like some additional information to help determine the next steps we should take.

1. Did Kid 1 have an available upgrade which you then used to upgrade Kid 2's device? (This process is called Transferring Device Upgrade Eligibility.)

2. You mention that there's a device that still has installments due. Are you referring to Kid 1's device, or Kid 2's device?

3. Is Kid 1's new plan with AT&T? 

If Kid 1's device has remaining due installments and her new plan is with AT&T, we'll need to Transfer Billing Responsibility to her new AT&T plan. This way, the financial responsibility will be moved to her new plan, and she'll be able to pay the installments. For additional information regarding Transferring Billing Responsibility, please visit our helpful article dedicated to the topic.

There are two parties in every Transfer of Billing Responsibility: the Initiator and the Acceptor. Once Kid 1's new plan has been established, you will need to Initiate the Transfer of Billing Responsibility, and she will then be required to Accept the Transfer of Billing Responsibility. After the Transfer of Billing Responsibility is complete, Kid 1 will be able to make her device installments on her own plan.

Thank you so much for participating in AT&T Community Forums, and we look forward to hearing back from you with more specifics so we can resolve your concerns!

Kiara, AT&T Community Specialist

Thanks for your help! I know it’s a bit confusing. 
I used kid 3 line to upgrade kid 2 phone. 
kid 3 then decided to get off my plan and get her own. So the line is no longer being used. The upgrade wasn’t her her though so she doesn’t need to pay the installments. 
kid 1 and kid 2 line is now clear for upgrade with no installment due on them. 

Thank you for following up, @vron87! No worries! We're here to work on this together and clear up any confusion regarding your unused line.

Any incomplete installment plan cannot be swapped between lines aside from being transferred to another AT&T plan. Therefore, the line can't be cancelled without accelerating the installment plan. If you choose to remove the line, the remaining unpaid installment balance will be due immediately. The balance will appear on your final bill. (This includes accessory installment agreements.)

Thank you so much for your participation in AT&T Community Forums, and we hope this addresses your concerns!

Kiara, AT&T Community Specialist.