Jim,
sorry for the frustration on the phones. We've temporarily been one man down in our support and the phones have been busy after the new data cycle. These are not excuses, just a temporary state of our office. We'll take measure to try and eliminate this from happening in the future. We'll also check into the phones and see why it dropped you.
As for the renewal, yes you will need to renew the Multi-Platform upgrade as well if you plan to continue using it on 3 total devices or mixing platforms.
Now for registering or de-registering devices. You can touch Menu -> About -> Account Info -> then touch the Edit option for your account, next you'll see a Change Email next to your email, touch it. On the next page that pops up there will be a Detach Device towards the bottom in the center. This will remove that device from your account. FYI, in our next release this is much easier. I hope this helps. If you have troubles, please feel free to contact our support team.