Stand-alone Apple watch not receiving/sending calls when placed near non-cellular iPhone

Hi,

I recently purchased a cellular Apple watch series 10 for a family member. The mobile service was activated through T-mobile. I created a separate Apple ID for this family member. I set up the watch using an Apple iPhone 12 with the same Apple ID. The phone does not have cellular service. The watch has its own mobile number. After the setup, I noticed that the watch the calls to (and from) the watch are failed. I retried the pairing process multiple times. The T-mobile agent told me to use my iPhone 15 which has cellular service (also through T-mobile) to set up the watch. So, I reset the watch and tried that also. But the set up process just hung. After several hours with the telephone agent, I gave up because it was late in the night and made an appointment with T-mobile to call me within 24 hours. But the agent did confirm that the eSim in the watch is active and it is registered under the phone number that was given to me for that watch.

I simply tried setting up the watch the next morning with the non-cellular iPhone 12. The set up happened without any issues. But, the same issue of not being able to make calls from the watch persisted. But the iMessage was working without any problem. I did a lot of research. I even called an Apple support person. But it was hard to make them understand that I am not trying to make calls away from the phone. The phone does not have cellular service. So, the watch should be able to access cellular service independently. I also checked the iOS on both devices. They were all updated.

The next day we were outside with the iPhone 12 left at home. Suddenly the watch started receiving and sending calls. I then realized that the watch does not seem to work independently if it is near the paired phone. It does not make any sense to me. I once again called Apple support and spoke to a higher-level technician. She told that if the watch is next to the phone, then it would only use the phone to make calls and not through the watch. It still did not make sense. I have an Apple watch (series 8) that does not have its own cellular service. It is paired to my iPhone 15. When I get calls, both my watch and my iPhone ring.

Lastly, if I had set up the cellular Apple watch (series 10) using my iPhone 15 as a family member, then will the calls be routed to my phone whenever the family member is close to me? So, I think if a watch has its own cellular service with its own phone number, it should act on its own without having the need of the paired phone. I certainly can turn off bluetooth in my iPhone 12 but that some of the apple watch apps cannot be updated.

I was wondering if anyone else faced this problem and was able to solve the issue.