  We show that a quantum clock cannot be teleported without prior
synchronization between sender and receiver: every protocol using a finite
amount of entanglement and an arbitrary number of rounds of classical
communication will necessarily introduce an error in the teleported state of
the clock. Nevertheless, we show that entanglement can be used to achieve
synchronization with precision higher than any classical correlation allows,
and we give the optimized strategy for this task. The same results hold also
for arbitrary continuous quantum reference frames, which encode general
unspeakable information,-information that cannot be encoded into a number, but
instead requires a specific physical support, like a clock or a gyroscope, to
be conveyed.
