The are currently with Sky for their FTTC, so was wondering if they move to FTTP (which I don't think Sky offer), how does the move work?
Actually, Sky have recently started selling FTTP. Just put their address in the checker
. It's currently offering me 80/20 for £25 or 150/30 for £35.
I would expect that if they phone up Sky, they should be able to arrange the transfer, assuming that Sky have an FTTC to FTTP migration process.
If they want to take FTTP from a different provider, then basically they are taking a new service from scratch, independent from the FTTC, which needs to be cancelled separately. The only thing which will cause the FTTC to be cancelled is if they transfer their phone number over to the new provider. When the new provider activates the phone number, it will automatically cease the PSTN line, which in turn ceases the broadband service attached to it.
This means you can do it using either of the two options that you described. If you want to run the two services in parallel for a while, which protects you against loss of service if the new provider messes up the FTTP install, then get the new service installed with a new phone number allocated.
Or, you can take a data-only FTTP service, and then later migrate the phone number to a VOIP provider, if you want to keep the landline service and number. The phone number then becomes completely independent of the broadband service, although you'll have to provide your own VOIP hardware (e.g. ATA or SIP DECT base station)
Also note that:
1. BT retail don't offer a data-only FTTP service. If you take FTTP from BT, then you must get a phone number, even if you don't use it.
2. If the ISP supplies voice over FTTP, this is *always* done via a PSTN port on the ISP-supplied router. No new services are being provisioned on the FVA (fibre voice) port on the ONT.