In short: Microsoft announced, shortly after Amazon's big hardware event, that it would be bringing Skype over to Alexa devices – primarily Echo devices. Allowing users to call each other using their Echo device. Skype users will be able to make and accept both voice and video calls over their Alexa device, of course, the video calls will really only work on devices that have a screen (i.e. Echo Show and Echo Spot). Microsoft says that Skype calling for Alexa will be rolling out later this year. There's no specific date yet for when exactly it will be available.
Background: Amazon has already rolled out voice and video calls to its Alexa devices, so Skype coming to the game is a bit late, but it is a welcome addition. Especially since Skype is so widely used, and there are likely many more people using a Skype account than having an Alexa device. Also users will be able to call phones and tablets using Skype on Alexa, instead of just other Alexa devices. Which is also a pretty big deal here. For both Amazon and Microsoft, this marks the next step in the collaboration between Cortana and Alexa. It'll be interesting to see what this collaboration brings in the future.
Impact: This is going to be a pretty big deal for those that are Skype users and also have Alexa devices in their home. Primarily because Skype hasn't been available on Alexa, so if you did a Skype call, you'd have to pick up your phone. But now with it coming to Alexa devices, you could answer the call on your Echo Show and have a much bigger and nicer screen to use for video calling – and as an added bonus, you won't need to hold the device while you are on the video call.