In various taxa, it has been shown that species regularly use grooming, i.e., an affiliative contact behaviour, to strengthen important social bonds. However, when group sizes become larger, this places a constraint on how much time is available for an individual to devote to grooming key social partners. Robin Dunbar’s social bonding hypothesis states that language evolved as a mechanism by which individuals can strengthen bonds over a distance when group sizes became too large to service important social relationships via affiliative contact. Here, I use association data, vocal exchanges, and affiliative contact behaviour data to test this hypothesis in wild male Indo-Pacific bottlenose dolphins, which form multi-level alliances that compete over access to females. Within the core alliance level, I found that allied male dolphins with higher bond strengths engage in higher rates of affiliative contact behaviour, while allied male dolphins with weaker social bond strengths engaged in higher rates of vocal exchanges. In addition, I found that males that were less well-connected within their alliance (low strength centrality) were more likely to respond in vocal exchanges. The findings presented here provide evidence that vocal exchanges can be used as a low-cost mechanism by which to service weaker, yet still vital social relationships. These results provide the first evidence outside of the primate lineage for the social bonding hypothesis and that vocalisations can function as a replacement for grooming when dyads are not in physical proximity. The results of the study herein raise important questions on the origins and evolution of language.