If not calls atleast text messages are possible with always connected pc's ?

I'd like to see that. You can text using Cortana from your PC, but if the PC is off you won't get text notifications. I wonder how these always connected PCs will handle that.
 
If telephony isn't enabled, I don't think text messages will be either.

You may be able to receive, in order to receive carrier messages but other than that probably not.