Hello,
just want to give my two cents quickly...
It was written here that no one knows what the future holds, etc. but the fact is already today that the classic telephone connection only exists with absolute old contracts or companies. I currently don’t know any internet provider where you don’t make calls via SIP, that is VoIP (Voice over IP), basically internet telephony. From that perspective, you could completely cut loose, for example Internet from Kabel BW, TV e.g. Sat, and telephone from sipgate.de or easybell.de. There is potential for savings if you know exactly what you want!
BUT, I would also have a Telekom line installed for 400 EUR. You never know what will happen with the pricing policy of the current providers, so: secure alternatives!
Best regards
splitti