Why won't my second line work after the update?

[Znoles4]

I have 2 cell phone lines and an iPad connected to my Apple ID. All 3 worked fine until I updated all 3 yesterday to iOS 9.01. The main cell line works and the iPad works, however the 2nd cell, my sons line, will no longer "activate" iMessages and although his phone number shows up as a choice, it does not let me choose this because it says an iPad is using this number. It only lets me choose my phone number. I have temporarily taken the Apple ID off of his iPad but it's still isn't working. Anyone know what the solution is?

[vzw_customer_support · Accepted solution]

Congratulations on the update. We are sorry to see this issue has popped up for you. We would like to help get that device connected to the ID. Please advise of any trouble shooting that has been performed. You can try this link to make sure that the device is added: https://support.apple.com/en-us/HT204074. We will be here for the results.
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