Depends on the IP Office level, though the fact that its still working hints that its okay.
The only bit of emebedded that is on the memory card (apart from the messages) is the prompts.
The way that the prompts got onto the card did change between 2.1 and 3.0 and so if you upgraded you IP Office between those level, then yes, you do need to change the prompts in the card.
However the rest of embedded voicemail operation is all part of the core software on your control unit and so upgrades with the control unit.