More people will be able to access the Alexa-Cortana collaboration their companies unveiled last year, now that the team-up is available as a public preview. Unfortunately, you can only take it for a spin if you're in the US, but this is still a much wider release than the limited beta Microsoft and Amazon rolled out a few months ago. So long as you're a customer based in the country, you'll now be able to summon Alexa through Windows 10 devices and Harman Kardon's Invoke speakers and Cortana through Amazon's Echo devices. The two tech giants are working together to bring the experience to more devices.
If you want to access Cortana on an Echo speaker, just say "Alexa, open Cortana" to use the assistant to check your emails, schedule and to-do lists. To summon Alexa on a Windows 10 computer, it's the other way around: say "Cortana, open Alexa" to play Jeopardy, add items to your shopping list, check your Amazon order status or to control your smart home devices.
Since this rollout is still just a preview, you won't be able to access some of the assistants' features on the other company's devices. You won't be able to ask Alexa to read an audiobook for you on a Windows 10 PC, for instance, and you can't ask Cortana to play music for you on an Echo speaker. The companies promise that the experience will become better and more robust as they become available to more people over time.