Someone posted a comment on slashdot a while ago on how they would prepare for such a situation like this by doing something along the lines of buying a new hard drive whenever they buy a new system and then cloning the hard drive that was included with the new system onto the new hard drive they bought and then using that separate drive as their primary drive in their new system. If their system ever needs to be sent for repair for any reason, they could just swap back in the original hard drive that it came with and the repair shop would not have any of their personal information, not even in the free space of the drive all without the overhead of using encryption. Although, it still might not be helpful if it is your new, separately purchased drive that needs to be replaced.
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You are assuming that conversions between file formats happens 100% accurately.
Someone posted a comment on slashdot a while ago on how they would prepare for such a situation like this by doing something along the lines of buying a new hard drive whenever they buy a new system and then cloning the hard drive that was included with the new system onto the new hard drive they bought and then using that separate drive as their primary drive in their new system. If their system ever needs to be sent for repair for any reason, they could just swap back in the original hard drive that it came with and the repair shop would not have any of their personal information, not even in the free space of the drive all without the overhead of using encryption. Although, it still might not be helpful if it is your new, separately purchased drive that needs to be replaced.
They don't appear to expire sooner anymore, at least according to T-Mobile's prepaid rates page. But, they still do cost more per minute.
Maybe you are looking for something similar to a cell phone signal booster?