But you can't actually simulate a TM on any machine with a fixed amount of memory. And any "special purpose" computing hardware would have at least a little mem

But you can't actually simulate a TM on any machine with a fixed amount of memory. And any "special purpose" computing hardware would have at least a little memory. So I don't think that distinction works. Unless it only applies to machines with expandable memory? Technically, if it were hot swappable, the memory would be unbounded. But nowadays, the SD slot on phones is often under the battery, if it exists at all.