Deutsche Telekom
Postado por Dora Böhm em Alemanha forum
But if this is for a new connection Alice can take 6-8 weeks to organise as they rely on Deutsche Telekom providing the line into the house, and Telekom don't like to be particularly efficient at providing this to a competitor.
Alternative is to take Deutsche Telekom for phone and DSL (min 1 month, thereafter 6 days notice to cancel, can be setup in 3-5 days)) and a no-frills provider such as JustDsl with 1-month cancellation notice.
Otherwise if you are planning to leave the country after your stay you could sign up with the provider of your choice, irrespective of the contract conditions and invoke an extraordinary cancellation as a result of your "unexpected" departure from Germany. Some may fight this, but their grounds for doing so are shaky.