I went to my local T-Mobile store and converted my iPhone 11 Pro Max from using a physical SIM card to an eSIM. The folks behind the counter fumbled a bit, but finally got my eSIM up and running and removed my physical SIM card. The day after that, we lost power in our home. It was a partial power loss, but we lost the modem and therefore lost WiFi. To my surprise, I was unable to use cellular data on my iPhone. It was as if I didn't even have it turned on, which I did. I tried a hard reboot, turned off WiFi and turned it back on. No WiFi, so that didn't do anything. Called the local T-Mobile office. They suggested resetting the Network settings. I did that. Didn't work. Called T-Mobile main line. Talked to tech support. They couldn't help and put in a help ticket. It was very frustrating that I didn't have cellular when my wife's iPhone XR was fine. Her phone could access cellular data. The next day, I was still frustrated. Power was back, but I still had this issue that needed to be fixed. I was finally able to fix it using the following technique.
1. Turn off WiFi on the iPhone.
2. Do a hard reset on the iPhone.
Once the iPhone came back up, it saw the cellular data. Now I can turn off WiFi and use cellular data. Not that I want to, but if I lose WiFi, it's nice to have the cellular data. Or, if I am out and about, I'll need the cellular data.
1. Turn off WiFi on the iPhone.
2. Do a hard reset on the iPhone.
Once the iPhone came back up, it saw the cellular data. Now I can turn off WiFi and use cellular data. Not that I want to, but if I lose WiFi, it's nice to have the cellular data. Or, if I am out and about, I'll need the cellular data.