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, BusinessWeek.com has learned. Sony BMG, a joint venture of Sony (SNE) 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.