I just installed "Reverb for Amazon Alexa" on my Android phone, It seems to work OK on Sprint's 4G network and it has Alexa's voice. I haven't been home yet to see how it works with my SmarThings hub, but the literature says it'll work just fine.
It shows up in the Alexa App as another device, but the caveat is it doesn't support music because of licensing issues. That's on Amazon's side. The developer is trying to work it out with Amazon
I don't know if it has been ported to iThings, someone with an iPhone might want to check the App Store.