No, the contract is tied to the number, so you cannot port a number to a new provider or attach it to a new contract.
You can add your plan to the Family Plan without affecting your contract dates though. Just have the Family Plan owner with you and call in to CS to have them do an Assumption of Liability. They will take over responsibility for the line and can add it to their family plan. Your plan will change, but your contract date will remain the same.
great thanks for the answer.
I am aware that I can move my contract to a family plan - but will my $40/month calling plan go to the $10/month or will I still pay full price? I guess I can get a new number if it doesn't work, but I'd really like to keep it.
Your line will be part of the family plan after the AoL, so it will be $9.99/month + any texting or data features that you want/need. You can change your plan at any time with no penalty.