Our app is a CallKit app. We handle supported calling flows in-app, but for certain numbers that we do not support, we fall back to native using a telephony URL. So the question we are trying to clarify is specifically about that fallback path: once the handoff to native telephony happens, is cellular line selection entirely controlled by iOS, and is there any supported way for a third-party app to influence or guarantee use of the line selected in Settings > Cellular > Default Voice Line?

Thanks both. I was confused because the APNs documentation page for sending notification requests currently says that the voip push type is not available on watchOS. We've now switched back and the watch successfully rings for incoming calls. That makes it seem like the APNs page wording may be stale.