Hi
If there is already a telephone line present, which sounds like there will be, then you have three choices for telephony if going for FTTP for broadband once it is installed. With overhead telephone cable they will replace that with a combined telephone and fibre cable so that the existing telephone line remains. If underground, they usually have room to just pull through a fibre only cable only running alongside the existing old copper wire.
1) Keep the existing copper phone line rental going. Telephone continues over copper, data goes over fibre. Might be more expensive as you are paying two bills, one for data and one for the copper phone line.
2) The way it will be in the future anyway, you ditch the phone line and just have FTTP then add a VoIP solution. This needs either an adaptor or new telephones that will plug into a router. The existing number can be transferred across to the VoIP supplier in most cases. You can opt for someone like SipGate that is free, you only pay for out going calls, but can receive free incoming calls for to the transferred landline number, or go with someone that charges a monthly charge for a package of calls.
3) Ditch a landline altogether and just use a mobile. This is something a lot of people will be doing more and more, certainly the younger generation will not be worried about landlines and many people already only have a landline because you get it automatically for broadband.
Obviously for most people 1 is the simplest most transparent solution as that is what they will already have and the data just moves to FTTP, but may cost more overall and in the next few years they will have to move to option 2 anyway.
As far as I know the telephone port on the FTTP modem is not in use and no products are sold to enable it, probably because Openreach want to stop being involved in providing telephony in the future, they just want to provide data.
Regards
Phil