I'm a current customer and need to purchase a new phone soon because my current phone is a very old Samsung Galaxy model that is functioning very slowly. I was about to purchase the S10 but under the current customer tab there are 2 options that confuse me and the difference between the 2 is over $200.00. There is an option to bring your own number that's $599.00 and upgrade your phone that's $699.00. What is the difference? I just want a new phone with the number I currently have and $599.00 is the more cost effective option for me. Why would I need to choose the upgrade your phone option?