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Background

I'm using an iPhone Xs Max, iOS 13.3.1.

I typically keep celluar turned off, and WiFi on. When I'm at home I automatically connect to my WiFi and can receive calls and texts no problem. When I'm not home, I can't receive calls or texts, which is fine by me -- and I'll only turn cellular on if I have to use Uber/Lyft or if I need to make an outbound call.

Issue

On very rare occasions when I'm away from home (and therefore connected to neither cell nor WiFi) I'll receive an SMS text. Usually just random stuff like Amazon sending me a locker access code, telling me I have a package to pickup, etc.

On even rarer occasions I'll receive a call in this mode. I can't actually answer it, but it'll ring once briefly and show me a caller ID.

Question

Why am I able to receive occasional SMS texts and inbound call attempts, despite cellular being off and not being connected to a WiFi network?

  • When you say cellular is off - how are you disabling all cellular communications? When you “keep cellular off” - it’s not likely shutting the radio as by law, emergency calls are always on so the phone always is talking to cellular towers or IMSI catchers or whatever else it around. – bmike May 2 at 17:57
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    @bmike Oh, I see. When I said I was turning cellular off, I just meant I switched the Cellular toggle from on to off in the Settings. So if I understand you correctly, even when cellular toggle is off, it doesn't turn the radio off. If I wanted to do that (not that I necessarily would), I'd have to go into airplane mode? – Yippie McSmashmouth May 2 at 19:30
  • Yes indeed - great question - an edit to the answer or your own answer explaining how you understood this would be ideal. Thanks for asking and clarifying. – bmike May 3 at 4:14
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Why am I able to receive occasional SMS texts and inbound call attempts, despite cellular being off and not being connected to a WiFi network?

Cellular data is not related to SMS. That's a function of your voice service. See: Cellular iPad-Air text message configuration for more details.

WiFi calling is a supplement to your cellular voice plan. If the WiFi network is available, your phone will use WiFi instead of the LTE network to make a call. If you turn off WiFi and cellular data and leave cellular voice on, calls will continue to come through.

But to summarize it, if you can make voice calls on your cell network, you can receive SMS/MMS messages.

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    Why the downvote? This is a perfectly reasonable and correct answer. – DavidSupportsMonica May 2 at 17:53
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    @DavidSupportsMonica This site is one that’s most stingy with up votes and least stingy with down votes. I believe the reasons are a mix, but in 8 years - that’s the pattern I have observed. It takes about 3 months to 2 years for the right amount of votes to find the good posts and even then there are many gems in the +3 / -1 range that I would expect to be +20 on other sites.. – bmike May 2 at 17:58
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    @bmike beat me to the punch, but yes, exactly what he said. I ignore it. – Allan May 2 at 18:00
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    @bmike Thanks to both of you. I'd not considered the time factor in an answer's collecting feedback. – DavidSupportsMonica May 2 at 18:42
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    OP, here. I didn't downvote the answer. Not sure whom you're referring to, but I'm showing +2 votes right now. I do have a follow-up question though. So if SMS is "function of voice service," and voice service runs over cellular, and cellular is turned off, and WiFi isn't connected, how could the inbound calls/SMS's come through ? Or do you mean that by turning cellular off, I'm not in fact disabling voice service at all, but just cellular data service? – Yippie McSmashmouth May 2 at 19:27

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