Elephants learn some of their calls through imitation, scientists report in this week's Nature magazine.
Elephant rumbles are known to be sophisticated and varied
They are the only land mammal, other than primates, that can undeniably copy sounds, the researchers claim.
The discovery was made when an orphan elephant called Mlaika, who lived near a road, was observed to make a series of convincing truck sounds.
Under normal circumstances, vocal imitation is probably used to cement bonds between elephants, they added.
"Elephants may be using their learning abilities to develop vocalisations similar to group members," said lead author Joyce Poole, of the Amboseli Elephant Research Project, Kenya.
Vocal imitation has already been observed in birds and marine mammals as well as primates.
Dr Poole believes it evolved to help maintain bonds between individuals in a socially fluid environment.
In other words, it helps two individuals remain socially close, despite all the comings and goings within their group.
"It may be, for example, that mothers and daughters have similar voices," said Dr Poole.
"And that could be one way how they recognise each other amongst all the different voices."
Although elephant rumbles are known to be sophisticated and varied, the phenomenon of vocal imitation was never observed before Mlaika's creative use of it.
The 10-year-old lived in a semi-captive group of orphaned elephants in Tsavo, Kenya.
Trucks were sometimes audible from her night stockade, which lay 3km from the Nairobi-Mombasa highway.
Scientists analysed her unusual rumbles and found that they strongly resembled truck sounds in frequency and pattern.
"These findings electrified me because no terrestrial mammals other than primates are known to be able to imitate sounds," said co-author Peter Tyack, from America's Woods Hole Oceanographic Institution, who normally studies whales.
"Birds, bats, dolphins and whales do so, but learning of a whole new animal group capable of vocal learning is fascinating."
After Mlaika, the researchers also found an irregular imitation in another elephant.
Calimero is a 23-year-old African male who has spent most of his life in a Swiss zoo with Asian elephants that make a distinctive and unique chirping sound.
Calimero also makes the Asian chirping sounds and not the deeper African calls.
"It will be very interesting to see whether African elephant groups have different dialects," said Dr Poole.
"But at the moment we don't know that."
Dr Tyack added: "Our paper demonstrates vocal learning and imitation, but only begins to open the door to a fascinating new area for research studying why elephants have evolved this rare skill."