I'd like to create a twin of my office extension at home so that I can not only answer the same call (e.g. ring group) but am also using the same voicemail. I've tried connecting two phones to the same account and password, but it seems that only one phone really wants to ring at a go, though both will make outgoing calls.
You can't connect two phones to the same extension. I suggest creating a ring group with one voicemail as the default destination. You can then reach that voicemail by speeddialing *98<extension>.