Amazon's Echo speakers can already play music from various sources, including Spotify, Pandora and its very own Prime Music. You'll need to stream tracks from a phone via Bluetooth for some of them, but some are already baked into the devices. A $5-month-offering that's limited to the speakers would likely appeal most to people who already have an Echo -- or have been planning to buy one for quite some time -- and don't really listen to music on the go. Its success depends on whether those people are willing to sign up for another service on top of the one they already have. Amazon has neither confirmed nor denied the product's existence, but we'll update you as soon as we find out.