The conversation in question was that between special envoy to the Russian president, Vladimir Lukin, and the commander of the Russian subversive group Igor Girkin (Strelok).
It became obvious from the conversation that Girkin coordinated his actions in Slaviansk city with the Russians. It means that the Russian Federation could have influenced the terrorists to release the hostages, if it wished so.
Moreover, as it became clear from the conversation, Girkin took advantage of Lukin's visit to Slaviansk for better preparation before the attack of Ukrainian Forces on Slaviansk. He coordinated optimal time for repelling the assault in the early morning of May 3.