They are different Skype accounts. In my opinion, the Skype Gateway is much more economical than Skype's VoIP service ($29/year/account for gateway vs $7/month/account VoIP), so I'd prefer to go that route.
Using the demo version of 3CX, I'm trying to setup multiple Skype accounts with great trouble. I can get either one to register by setting one as a master, but never both. I hope somebody can help!
See attachment for details.