> Both use the same underlying technology (XMPP) and both know how to use the protocol, but it's still very hard to pull off at this scale once you allow multip

> Both use the same underlying technology (XMPP) and both know how to use the protocol, but it's still very hard to pull off at this scale once you allow multiple devices to login with the same account. Since when does Skype use XMPP? AFAIK, it uses a closed protocol. It appears that Whatsapp does indeed use XMPP under the hood, though. As for Skype, it's absolutely terrible at handling multiple devices. It would get much better if the app phoned home when a given message arrived on a Skype client with a focused window, in order to prevent/cancel already existing alerts on other devices.