If you travel a lot, or if you are frequently within Wifi range during office hours, then the Advanced option is definitely worth considering. You can call any number via the R4Telecom service from an IOS (Apple) or Android device, from the Netherlands or abroad. Do you want to use the service from another device? Then you can simply use the "call-back" option. This allows you to control which (fixed or mobile) device the call takes place from your mobile device.