I'm using iPhone 13 with iOS 16.3.1 and Verizon Wireless.

In my office, the WiFi signal is very strong, but cell signal is weak, i.e. between 0 and 1 bar most of the time.

From some googling, I understand that if I have "WiFi calling" turned on, it's supposed to use WiFi to send green bubble SMS too. However, instead the green bubble messages I send are very flaky, i.e. they only get delivered like 1/3 of the time, and the other 2/3 of the time there's a red (!) icon next to the green bubble, which says "not deliver"; I have to constantly toggle Airplane mode on and off to get the cell bars higher and then sometimes it works.

In contrast, blue bubble iMessages work fine. Also, when I'm outside on the street and I have five bars with 5G, green bubble SMS also work fine.

Am I doing something wrong in the "weak cell strong WiFi" case? Isn't turning on "WiFi calling" supposed to make sending green bubble SMS texts just as quick and snappy since I'm on a strong WiFi connection?

  • Force your phone to use only WiFi by turning off cellular. If you have a signal, even a weak one, it will try SMS first and not necessarily fall back to WiFi.
    – Allan
    Mar 3 at 14:29
  • You can turn off cellular in Control Center by pressing the green button with an antenna icon. I’ve done this before and it worked. How did SMS instantly fail? What message did it give you?
    – Allan
    Mar 3 at 15:09
  • SMS does not use cellular data; MMS does. So turning it off as you describe has no effect. Verizon might be preventing messages being blocked that don’t originate on their network. Check with them fir details.
    – Allan
    Mar 3 at 15:51
  • (deleted all my previous comments) TLDR: tried airplane mode with wifi on, toggling green antenna button, none of which work. If Verizon really prevents all SMS that don't originate from their network, and my wifi router obvious does not count as Verizon network, then by definition SMS by wifi doesn't works. Have you confirmed that SMS works for you? i.e. when you're in a very weak cell signal but strong wifi signal area, you can very easily send SMS?
    – xdavidliu
    Mar 3 at 23:42
  • I sent a message to an Android user today with Cellular off and it went through. I use AT&T
    – Allan
    Mar 4 at 2:30


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