Since in oscine birds song divergence often leads to premating reproductive isolation, we asked which factors drive the evolution of song in a widespread species, the coal tit Parus ater. Based on an almost taxon-complete phylogeny we correlated song divergence with morphometric (ecology), genetic (time), and geographic distances (separation). We found eight well-supported mitochondrial lineages, one of which consists of melanolophus (usually treated as a separate species) and whose relationships remain generally unresolved. Due to intense song variability even sophisticated sonametric analyses failed to separate sub-specific units. We tested for the role of song in reproductive isolation by playing songs from China and the Himalayas to Central European males. They recognize them as conspecific, but react to their playbacks less aggressively than to local songs. While morphological divergence is correlated with neither time nor separation, song divergence coincides more with geographic than genetic distance. This is mainly driven by differences along longitude and is especially prominent in the southern part of the species’ range, where six lineages persisted during the last glaciation while the north was subsequently re-occupied by two lineages.