Hi Dave, thank you for your quick reply!!
I'm well aware of VOIP solutions and Skype plan offers, but i have this cell phone plan which allows me to call for no cost, and navigate 4G until XX GB. I just wanted to use my SIM card directly into the surface and make calls (directly from my surface)... like with windows mobile... using my personal cell phone number.
Simple as it seems, I suppose microsoft didn't think of it.
By the way it's such a simple operation that is supported even in iPads from Apple, so I was sure Microsoft would have put that possibility on a premium device such as the Surface Pro...
By the way I won't use internet connection to make calls, since calls are in my plan and it would be really dumb to waste GB. Probably the only way is to keep the SIM in my phone ad use it as hotspot if I ever need internet in my Surface.
At least until Microsoft make a dedicated app to call your contacts :-)