Chances are, as smartphones were making their impact in the consumer marketplace, Pandora was the product that introduced you to the idea of music streaming. Their business model in the beginning was popular with music fans: unlimited free music with only occasional commercial breaks. The music worked similar to how a radio stations work, but on a much more personal level. If you dislike a song, you aren't forced to listen to it every hour.
Similarly, Sirius and XM Radio, now a single company, had a unique business model. For a small monthly fee you received a large selection of unique radio stations that were always available no matter where you went (so long as you could see the sky). This was popular with travelers and homebodies alike. You could get a large variety of music without commercials, as well as talk from Oprah, Howard Stern and more.
Over the past few years, both business models have had their troubles. Pandora has tried to reinvent itself several times, with little to no success. Because of that, sources have come forward to say that SiriusXM is currently in talks to acquire Pandora, which would add a more diverse streaming structure to SiriusXM's existing online platform.
Pandora has been in search of a buyer for a little while, and rumors suggest that they are looking to close a deal within the next 3 weeks. If that is the case, SiriusXM's bid could potentially be successful. The real question, of course, is whether or not the merger will be a success. Two companies that have both failed to retain their market leads merging can work, but more often it simply compounds the issues.