Ugh! Your phone wants to configure itself for a cellular network. The SIM in your phone is provisioned for cellular service with Sprint. Sprint’s network is CDMA. Unless you want them, I’ll spare you the details on CDMA. What I will say is unlike the U.S. there are no CDMA cellular networks in the U.K. U.K. cellular networks use a different technology (GSM), which is why I believe the attempt for configuring to a cellular network is effectively looping. I had hoped disabling the cellular radio (airplane mode) would stop that.
Here’s a shot in the dark that may or may not help. When presented with the first message (which comes from the Republic Wireless app), since it’s the only option tap OK. If I’m understanding correctly that brings you to the second message (which comes from the background app “SprintDM”. Tap Cancel on that one. Tap the square lower right to bring up a list of recently used apps. Tap the X in the upper right of SprintDM, so that it’s dismissed from memory.
With all that done and before attempting another phone call, please try a VoIP reset as described by Republic here: How to VOIP Your Phone – Republic Help. Ignore the references to Lollipop 5.1 as the process for newer phones hasn’t changed. Finally, restart your phone.
Additionally, you reference dialing U.S. numbers. Republic phones only make outbound calls to U.S. and Canadian numbers. You are unable to make local calls in the U.K. with the Republic SIM resident in the phone, correct? I just want to be certain your phone isn’t doing anything else strange.
You also reference your home in the U.K., so would it be accurate to say you split time between the U.S. and the U.K? Depending on your U.S. location, it might make sense to switch the cellular network provisioning on the phone from Sprint to Republic’s GSM network partner. A zip code where the phone is used in the U.S. would help us to determine if this might be a valid path forward.