What do you mean by "original SIM"? As far as I know, SIM cards have always been specified in functional terms, so vendors were always free to implement them whatever hardware and software they choose, as long as the result complies to ISO-7816 and the relevant ETSI/3GPP specifications.
Today, it's mostly Java Card implementations, meaning that the ISA and smartphone OS/runtime is abstracted away in any case.
Today, it's mostly Java Card implementations, meaning that the ISA and smartphone OS/runtime is abstracted away in any case.