What is the difference between upgrading to a family share plan and a new family share plan on the account? If you upgrade your current individual plan to a family plan, you will have one family plan that includes the new line you added when changing your plan. If you add a new seperate family plan on the account, you will have two plans on your account: your current individual plan and the new family share plan. This would be substantially more expensive, and in most every case (unless you need more than 5 lines), you should just change to a family plan.
I'm wondering cause I would like to add someone to my account and possibly upgrade my phone at the same time. Would I incur charges? Changing plans is free. Adding a line may require you to pay an activation fee for that line, as well as any cost for the phone you buy when you sign the contract. You will only be able to upgrade your phone at a subsidized price if you are currently available for an upgrade. Each line on a family plan has its own contract, and your contract end date will not change just because you added another line to your plan.