The green socket is effectively the same as your current copper master socket. DV phones just connect to the hub via DECT, the hub is a DECT base station.
https://community.bt.com/t5/Home-phone-including-Digital/Digital-Voice-FAQs/td-p/2207485
C to P? that's a new one on me, I'd be very interested in finding out what it means if anyone knows
FTTC to FTTP presumably?
This seems like the most logical explanation yet...
Whether this is the case or not, it would be useful for BT to actually say what they mean as it helps everyone. There are far more knowledgeable people than me on this forum and the search has drawn very little.
If *All the order says with regard to the equipment is "C to P Welcome Package" and "Alexa Advanced Home Phone"* that means you aren't getting a new SH2.
The C to P welcome Package (presumably C means Cabinet as in FTTC and P means Property as in FTTP) is an ethernet cable that will allow you to connect the WAN port on your SH2 with your ONT.
I believe some early SH2s do not have the green phone socket
So my C to P welcome package turned up today & consisted just of a RED ethernet cable for the red WAN port on the back of my newer Hub2. And a little piece of paper & a paperclipped WAN sticker explaining this is all I need to give to my engineer to fit full fibre during the appointment.