A contradictory term, as no one person ever speaks for the Borg.
The Borg, arguably the most powerful race in the Star Trek Universe (minus Q who isn't considered a 'race', but an entity). The Borg originate somewhere deep within the Delta Quadrant, where the Federation starship Voyager spent a majority of time.
The Borg are able to possess such firepower, strength, and regenerative capabilities, due to all Borg being interconnected on a mental scale. The mere thought can direct billions of Borg to repair a damaged portion of the ship. This power allows for seamless interactivity among all Borg drones, and thus, no conflict ever arises.
The mere presence of individual thought, one individual questioning the wishes of the collective, has shown to be catastrophic. In the time of the Enterprise-D, a solitary Borg drone garnered the attention of the Enterprise, located in a crash site within the Argolis Cluster. This Borg, dubbed Hugh, by the Enterprise crew, had it's link to the collective disconnected, however, remained alive and able of thought processes. This Borg, by help of the Enterprise crew, developed a personality conducive of an individual and eventually retrieved by the Borg collective.
Later in the series, a return appearance by Hugh showcased the effect on the Borg that individual thought has. Routine tasks left undone; ships found drifting in space, drones self-destructing. Hugh's Borg ship that retrieved him virtually destroyed by the individual thought Hugh introduced, and thus, drones started to question their purpose in the collective.
Hugh is just one of two examples of when individual thought was shown within the Borg collective. The other example was when the Borg queen made her appearance in the movie, "First Contact." The Borg needed a spokesperson to communicate and appeal sexually to a recently emotional Data. The Borg queen, also seen attempting to convert Jean-Luc Picard, then dubbed Locutus of Borg, has a history of appearing when the Borg require a spokesperson for the collective.
In all aspects though, the term 'I' muttered by a Borg is a contradictory term. The collective abhors the use of single pronouns, and refers to themselves as 'we'. If you ever hear a Borg say the term 'I', or any term for that matter, it will be far too late to do anything about it.