Seems like I will be having a 'frank and meaningfull conversation ' with TT.
There's no conversation to be had, unless you can convince them to change the product they sell.
There's simply no way to "upgrade" to Talktalk FTTP residential and keep the landline number.
It's been tried numerous times on the Talktalk forums and on ThinkBroadband.
An upgrade simply makes the landline number disappear.
**The only way is to migrate the number to VOIP, and then take FTTP as a new customer as it ceases the FTTC.
** It can be done with a break in service.
Migrate FTTC landline number to a 3rd party VOIP provider. This ceases your Talktalk service.
The day after the line is ceased you can order FTTP from the closed account.
There's downtime between the FTTC ceasing and FTTP being installed.
Alternatively there's Talktalk Business. You can migrate a residential account to business.
In fairness to Talktalk the sales team are very clear in their explanation during FTTP ordering that it is a data only product and you can't keep your landline number.