The term data roaming is used to describe the practice of using mobile data transfer services supplied by one mobile service provider via a telecom network provided by a different mobile service provider. It is most widely used to describe the use of mobile data while traveling in a country or region which is not serviced by the mobile service provider which supplies the SIM being used.
Data roaming differs from call roaming and SMS roaming in that it makes use of data services rather than telephone services.
Example of data roaming: When you use a SIM provided by a Swiss mobile service provider when you travel outside of Switzerland, your phone connects to a local mobile service provider in the country in which you are traveling. If you connect to the Internet (including chatting or voice calling through Internet-based services like Whatsapp) while your phone is connected to a foreign mobile service, you are using data roaming.
When you access the Internet while roaming on a third-party network, data requests are transferred from your mobile device to the third-party mobile network which you are connected to. From there they are transferred through international transit services to your home network (the mobile service which provides your SIM), which transfers them to the Internet. The data is then retrieved from the Internet to your home network, forwarded through international transit services to the third-party network which you are connected to, which transfers it to your mobile device.
Because at least three different service providers (your home network, international transit services and the foreign network) are involved in this process, data roaming typically incurs fees from all three service providers. For this reason, data roaming is normally more expensive than using mobile data in Switzerland (in which case data is transferred to and from the Internet directly through your home network).
Charges for data roaming are included in your phone bill if you use a mobile plan, or deducted from your prepaid credits if you use a prepaid mobile service.
Data roaming and Swiss mobile telecom service providers
Swiss mobile service providers have agreements with foreign mobile networks which make it possible for customers to use roaming services in most countries around the world. In some countries Swiss SIM users can use call roaming, but not data roaming. With Swiss SIM cards, data roaming is typically enabled by default. It can generally be disabled upon request.
Data roaming costs
Data roaming can be extremely expensive, particularly when its used at standard rates. Many Swiss mobile service providers offer data roaming bundles or options which enable data roaming at prices far below standard rates. You can use the roaming calculator on moneyland.ch to find the exact data roaming rates for data roaming in a specific country with your mobile plan or prepaid service.