According to the developer of the mod the sounds in Minecraft PE is already a coded feature. But since the size of songs are too big they haven’t been added as an available feature yet. But if we remember it correctly it has been mentioned by Mojang that it will be a likely addon in the future.
By using this mod you can access the Minecraft songs (which are the same songs available for the PC version of Minecraft). There are tens of different songs which will load both on the start screen and in your Minecraft worlds.