Sounds like the US is a little more annoying to get things done then here in the UK, if you want a new sim (in this case microSIM) all you have to do is ask for one to be sent, and if you are good at talking your way or have a nice operator, you can get it for free. And when it arrives you just pop it in and they will have given you a time for your current sim to deactivate and the new one activates. All your details are instantly associated with the new sim card and your original plan, regardless of whether they offer it to new customers now or not, will be on your new sim. I.e. long story short, you can get a new sim with everything as before her ein the UK so long as it is during your contract and not at the end of it.