  Suppose that $m$ senders want to transmit classical information to $n$
receivers with zero probability of error using a noisy multipartite
communication channel. The senders are allowed to exchange classical, but not
quantum, messages among themselves, and the same holds for the receivers. If
the channel is classical, a single use can transmit information if and only if
multiple uses can. In sharp contrast, we exhibit, for each $m$ and $n$ with
$m\ge 2$ or $n\ge 2$, a quantum channel of which a single use is not able to
transmit information yet two uses can. This latter property requires and is
enabled by quantum entanglement.
