I got an upgrade offer. The only question I have is related to the plan. I'm a bit confused when I add the phone to my cart, it says plans start from $45. Can I use my current plan or is that plan only for my current phone. I came over from Public Mobile, so I have the $40 plan. If all I'm getting is a discount on a phone and have to start with one of the regular plan,then I'd prefer not to lose my plan.