I have seen a lot of posts about activating new lines for certain deals like credits, rebates, free phones, etc. In most cases people then need to port the number out to avoid a cancellation fee but the port can cost money. I searched and found Sideline which ports your number out for free.
I don't think this would be good for multiple ports but if you are just porting one line out like I was it can work.
Edit: Please note that I made this post as a free option to port out an unwanted number (that I acquired during the recent Target/Verizon new line/gift card promotion) without having to pay a port or cancellation fee. I do not plan on using the sideline service nor do I know how well or poorly it works.