| Common mode of phone usage and even internet access in Germany: while the vast majority of people still use ex-monopolist Deutsche Telekom as their phone provider, they can use cheaper long distance call and internet rates offered by other companies without any kind of application or paperwork. This is done by using a company-specific phone number prefix for long distance calls. In the case of internet access, this is not necessary; there, the second defining characteristic is the only one: payment is done through the monthly phone bill from the Deutsche Telekom, which keeps part of the money for this accounting service and for providing the last mile lines.
The name "call by call" (used like this in German) is derived from the fact that this practice allows one to use a different service provider for each individual call or internet connection - normally the cheapest one. Since rates vary a lot with the time of day, people rely on tables published in newspapers that list the cheapest provider for each hour of the day. Some even invest in a least-cost router which does this automatically. | 
