To me the real question is whether any particular virus lineage evolved independently, or started out as an organelle or other apparatus of a cell, and got loose.

I doubt we will ever know, about most viruses, because they evolve so fast. But it would be seriously cool to find a bacterium using them for communication or as an extra-cellular library.

We already know about plasmids, of course, and there are plasmid viruses that dispense with the protein wrapping. But do any bacteria communicate, or store information in the environment, via non-viral genes wrapped in a viral protein coat? Would we notice if they did?

We still would not know whether the bacteria co-opted a virus, or developed the mechanism by itself. Indeed, it could be that the original developer of, say, those mosquito-shaped phages was wiped out when they went rogue.