I have only used mobile modems for data so far, so my info is from the internet, but Gnome calls should support normal phone calls. However, it uses modemmanager for this, so it has to work first. So maybe it hides that option from you, i do not know.
Which on the other hand means all you need for calls is modem manager and a sim card and modem supporting voice calls and the modem to support voice over usb (not all do) and according to some guides you should be able to make and receive calls from command line (or gnome calls as gui).
Also see what i wrote here.