This forum has a great deal of expertise and probably has the answer to this question.
The most significant difference between a Nuvi 855 and and 885 is Bluetooth for the 885. Plus traffic.
Both of these units have voice commands and have a Remote Switch which activates the Nuvi listen mode.

I assume maybe incorrectly that the Remote Switch is a Bluetooth device so maybe even the 855 has everything there for the Bluetooth option to work it just need some extra 885 (Bluetooth related) files to activate this function for the user. I notice that the Test Pages have a bluetooth option just nothing happens when you select it.

Are these files available or can they be extracted from the last 885 update files?
I realize this is an old 800 series Nuvi but it has many features and option just looking to add the rest to the 855,
Thanks for any assistance or comments.