3CX works with Skypes SIP service, if that is what you want to use. This service was limited to business, not sure on the current status, or if you plan on using for personal or business use. There is/was a 3CX Skype Gateway that allowed calls to "regular" Skype users, and if you have credits, to landline numbers as well. I suspect that this is what you are talking about.
http://www.3cx.com/voip-gateways/skype/
However...this is no longer supported, not to say that it won't work, but you are on your own (no 3CX support) if you can't get it to work, especially on a newer version. Note that it requires that you use an older version of Skype, once you have that , be sure it is set not to update.
That said, I currently have it running on version 11 with no issue, and I did have it running on an early version of 12. I can't speak for the updated version.