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Microsoft is reportedly killing Skype
(www.windowscentral.com)
This is a most excellent place for technology news and articles.
You can do this using JMP Chat, which bridges phone numbers to XMPP. Unfortunately, it's USA and Canada only, for now.
Alternatively, you can use a "SIP Trunk Provider". For instance, in the UK, Andrews and Arnold offers this service. You can then connect any compatible SIP client (e.g. Gnome Calls).