This is not a good video of it, but there are some really bad N900 copies which have 2 sim card slots on the back.
These fake N900s do not have Nokia standard build quality, and although they have a skin to look like its running Maemo, its not actually running maemo5, but they do have working dual sims.
These are useful for crossing China/Hong Kong/Macau where all use different telephone networks, or just for dual business/personal numbers.