Though the rules as written might technically permit someone with Leadership to gain 40 bards as followers, I would put the kibosh on having the bardic music transmitted through a magical walkie-talkie. It reeks of abusing the rules, and gives the player and the party a very large advantage. I always viewed followers as a sort of passive resource for the PC. Unless your adventuring party doesn't do a lot of roving, having 40+ followers trailing their leader through the dungeon is sort of absurd (and would lead to a lot of death). Having your followers maintain a home base, whether that be a keep, school, library, laboratory, temple, or something similar, that's fine. That's a resource the PC and party can draw on periodically (research, healing, social connections). But putting everyone to benefiting the party constantly strikes me as unfair, as in taking advantage of them (which could lead to a decrease in followers). Being the boss' orchestra or back-up singers might be cool at first, but being constantly "on-call" would take a toll on all of those guys. Both mechanically and flavor-wise, I would disagree at allowing it to be used in that fashion.
Now, RangerWickett said this DM isn't worried about breaking the system too much, so this may be moot for this DM.