Voice on Nokia 225 no longer working.

@syaoran The one I've gotten only shows one sim slot. I know the device is said to be dual sim but mine only has one. I never worried about this though since the phone was working fine on the network up until recently.  I don't know if any updates to the handset.  I had just voice and text plan with T-Mobile that doesn't have data.  

@fireguy_6364 Yes, I believe I'm still getting 4G as my service indicator on the device lists 5 bars of LTE.  

T-Mobile uses Google’s stock implementation of Android’s VoLTE and WiFi Calling.  This goes all of the way back the G1.  If Google has changed something, it would affect a lot more users.  Have you had an update with the device recently that might have impacted VoLTE working on T-Mobile?  The device is a dual-SIM device.  Have you tried putting your SIM in the other slot to see if that helps?  Some dual-SIM devices only allow certain features to work on a specific SIM slot.  

Not being a T-Mobile sold device.  It probably does not support the stock implementation of VoLTE that T-Mobile uses and can no longer fall back to 3G to make a call.  VoLTE is required to make calls now after the 3G network shutdown.  If your device does have a VoLTE setting that isn’t enabled.  Try enabling it to see if that resolves your issue with calls.