One of the great advantages of having an app that works on the internet means that it works in exactly the same way, wherever you have access to the internet.
Once our app registers it still thinks it is in the UK and continues to accept calls in the same way without roaming charges*
Similarly, the outbound rates you pay are the same in whichever country you happen to be in.
You can also save money by using Virtual Landline to send text messages at only 4p a time which is much cheaper than any roaming tariff.*Please note, that using 4G/3G data to make and receive calls may end up costing you more in data roaming charges than you are saving on the cost of the call. For safety, only use free Wi-Fi service when overseas to avoid unknown costs. Similarly, you can send SMS messages for 4p each from anywhere in the world, but the return path uses your normal GSM mobile account, so you will still pay return/inbound SMS message in the normal way.