  We study the effects of quantum entanglement on the performance of two
classical zero-error communication tasks among multiple parties. Both tasks are
generalizations of the two-party zero-error channel-coding problem, where a
sender and a receiver want to perfectly communicate messages through a one-way
classical noisy channel. If the two parties are allowed to share entanglement,
there are several positive results that show the existence of channels for
which they can communicate strictly more than what they could do with classical
resources. In the first task, one sender wants to communicate a common message
to multiple receivers. We show that if the number of receivers is greater than
a certain threshold then entanglement does not allow for an improvement in the
communication for any finite number of uses of the channel. On the other hand,
when the number of receivers is fixed, we exhibit a class of channels for which
entanglement gives an advantage. The second problem we consider features
multiple collaborating senders and one receiver. Classically, cooperation among
the senders might allow them to communicate on average more messages than the
sum of their individual possibilities. We show that whenever a channel allows
single-sender entanglement-assisted advantage, then the gain extends also to
the multi-sender case. Furthermore, we show that entanglement allows for a
peculiar amplification of information which cannot happen classically, for a
fixed number of uses of a channel with multiple senders.
