Status of SIP client

I’m evaluating a bunch of scenarios for the SignalWire platform. Here’s one I’m hitting walls with.

I have an app, a user will have a number they buy in the app (hosted by SignalWire). As a user of my app, they want to filter calls (and texts, but that’s much easier). If it’s from their friend, they want it to go to the SIP client app on their cell phone. If it’s from a stranger, they want it to go to their desk SIP phone.

However, if their desk SIP phone isn’t working, they want their cell phone app as the backup.

I need to determine if a given SIP client is connected/available. I’m not finding anything in the REST API that has that, so the webhook providing the XML response can’t get that information.

Am I missing something? Should I have a different approach?