There are 2 options:
A) the normal Internet connection, sometimes sometimes (limited by time of day) sometimes slower when many people are on the Internet,
is cheaper, and works, .. only sometimes slower
B) Glasfaserkabelda you have to expect monthly fee with ca (depending on the offer) between 60, - and 70, - Euro, this varies at the time with many telephone providers extremely with different conditions and tariffs. But you have high speed Internet.
Therefore one should inform oneself accordingly with at least 2 or 3 different offerers.
Mobile: There are 2 options:
A) a mobile phone with a contract, so then cheaper to call advantage
Disadvantage, you have a fixed minimum fee.
B) a mobile phone to recharge (eg in the SPAR market at the cash register, and in telephone transactions)
then you only pay the recharge, but the phone calls are much more expensive.
and you have to charge at least the phone every 3 months with money, it remains up to each one, for how much money, ... at least 5 € ....
Again, there are fluctuations that force the providers at different rates to recharge the phone. If you rarely call on the phone, you will otherwise lose credit.