In a move that would mark the end of a digital music era, Sony BMG Music Entertainment is finalizing plans to sell songs without the copyright protection software that has long restricted the use of music downloaded from the Internet. Sony BMG, a joint venture of Sony and Bertelsmann, will make at least part of its collection available without so-called digital rights management, or DRM, software some time in the first quarter, according to people familiar with the matter. Sony BMG would become the last of the top four music labels to drop DRM, following Warner Music Group, which in late December said it would sell DRM-free songs through Amazon.com"s digital music store. EMI and Vivendi"s Universal Music Group announced their plans for DRM-free downloads earlier in 2007.