The term call roaming denotes the practice of making phone calls through a mobile service provider from one country or region while traveling in a country or region serviced by a different mobile service provider.
In call roaming, the SIM card is not switched for a SIM card from a local service provider when the user travels to a different region. Calls are serviced by the SIM card provider in collaboration with third-party mobile service providers in the visited countries or regions. Call roaming, together with data roaming, forms the bulk of roaming services offered by telecom service providers.
Example: When you travel outside of Switzerland but continue to receive or make phone calls to or from your Swiss phone number using your Swiss SIM card, you are engaging in call roaming.
Making voice calls through an Internet-based service like Whatsapp or Skype while traveling abroad does not fall under the call roaming description because calls are not channeled through conventional telephone networks but through Internet servers. When you use these services via a local Internet connection (a WLAN, for example), you are not roaming at all. When you use these services via the mobile data connection provided by your Swiss SIM, you are using data roaming.
Charges accumulated by call roaming are either added to your phone bill (if you have a mobile plan) or deducted from your prepaid credit.
Call roaming from Swiss service providers
Today, Swiss mobile service providers provide call roaming in most countries around the world. Call roaming is typically enabled by default, and disabled upon request.
Call roaming rates
Like data roaming, call roaming can be very expensive – particularly at standard rates. You can drastically reduce the cost of call roaming by using supplemental roaming options or bundles.
The mobile roaming calculator on moneyland.ch makes it easy to find the cost of roaming in a specific country using your mobile plan or prepaid service, and clearly shows available options for cutting the cost of roaming.
More on this topic:
Roaming calculator
Call roaming tips
Deal of the Day 
