changing second line phone number

[rods]

I have need of a phone number in NC now. In some weeks, I want to change that to a TN phone number. I will no longer need the NC number.
How do I do this?
What does it cost?

[Mojo]

If you want to select a NC as your second number, you can go ahead and do that in the Lounge (if you have Premier). If you want to change that number later, it costs $11.99 (to cover the cost of the provisioning of the outbound caller-name).