You say 'clam shell' I say 'small laptop'. Whatever software is developed/used for telephony will be usable across distros. What is far more pertinent is the desktop environment
/window manager being targeted. Not many people make phone calls from a Linux desktop so there is definitely some development to be done.
I think that people go overboard when they think that use as a phone dictates needing an entirely different DE. All it really needs to be is a single 'Telephony' application.
Open it, it goes full screen. In Psion fashion a horizontal row of telephony function icons run left-right at the bottom of the screen.
Messaging selected, messaging 'from who' contact lists on the left, content of the highlighted message on the right.
Phone selected, recent contacts list on the left, dial pad on the right.
Contacts selected, contacts list on the left, highlighted contact's details on the right.
Minimize it or close the lid and it runs in background. It is a Telephony application that we need, not a new DE.