If you use the Horizon or CallSwitch mobile apps on your Apple smartphone and are on the EE mobile network you may experience problems with connecting calls whilst using a mobile data  ( as opposed to a wireless Wi-Fi ) connection.

 

The reason for this is that EE have changed their mobile data to work with IPv6 by default (as opposed to IPv4) and some changes within IOS 12 ( in particular ) are stopping the Horizon and CallSwitch mobile apps working correctly

 

The work around potentially is to set the mobile network APN to IPv4 by default but we have yet to find a way to do this on an Apple device.

 

The network providers are working on a solution