You can use telecom providers' services in two different ways. The easiest is preselection: Just register with a provider and all your calls will automatically be with this provider. Every customer can determine a preselection provider. However, ADSL customers are often obliged to use their ADSL providers preselection. In this case, you may use Call-by-Call.
Another possibility is Call-by-Call: The customers can dial a 5-digit provider code before every number to use the selected provider instead of the preselection provider. Call-by-Call providers often offer attractive deals especially for international calls.
You need to register with the provider for both preselection and Call-by-Call. You can register through comparis.ch for most providers.
