From when at the earliest are cables installed in a prefabricated house?

I have a house number ;)
At least it’s on the notice for the recurring charges.

Do you or anyone else know how it works if you only want the line, but no contract.
Regarding costs, handling, ...

Sorry, I have to intervene here: Whether you have a house number is totally irrelevant to Telekom. Your house number must be recorded in THEIR system – and for us alone, that took 2-4 months and about 20 calls (well, we are Vodafone customers and wanted something from Telekom,...). So it’s not enough that you have one (or don’t) – they must have created one for you.
For us, the cable was laid by E-On and they also connected it to the Telekom network – that worked out really well. The installation of the house connection by Telekom then only took another 2 months.

I think that sounds like a call to the Telekom-Bauherren Hotline! When we connect the duct, we will lay corresponding empty conduits that the utility providers can use. I am curious because I want to move away from Telekom but still keep the connection, as the 50MBit I have now cannot be maintained at the new location.

Line and contract are two different things. If you have the handover point attached to the outside of the house, it costs nothing; installed inside the house around 360 €.

Even if it costs a few euros more, he will come into the house. Thanks for the info. I have already had the initial contact with Telekom regarding the inquiry, but the construction was delayed. Somewhere at home, I have the number of the company that installs the connections for Telekom at our place. I'll just inquire.