That's … not how it actually works if you are in Germany. Typically you get a flatrate or minutes to landline and two prices for mobile calls: One for calls to your carrier, one for calls to other carriers. You might, for examle, have 120 minutes for calls to people with your carrier and 19 cent/minute to other carriers (and if you go over the 120 minutes).

It's actually not so complicated, but it's certainly often a good idea to know which carrier someone is using when you are calling them on the mobile phone. There are, however, also plans that treat all carriers the same.