We have an old iPhone 5 at work that is used as a general incoming-calls phone. It’s used for very little other than just making and receiving calls.

In general, its reception has always been good and stable, with no unexpected problems.

Lately, however, an issue has started repeating with annoying frequency: when we receive a call and pick up the phone, the conversation goes smoothly for about 20–30 seconds or so, then you hear three short, rapid bleeps (‘doot-doot-doot’), and the connection is dropped. A few seconds later, the signal strength indicator at the top of the screen says “No signal” for about 10–20 seconds. Then full signal comes back and you can continue to make calls as usual.

I haven’t experienced this issue when calling out—only when receiving calls. When calls are not being made, signal strength also seems to be normal (at least I haven’t noticed it cutting out at other times).

The actual signal strength is excellent, so it’s not because of dodgy coverage. We have about ten other phones, both iPhones and Androids, that manage just fine, and this is a recent issue with this one phone as well. Wifi signal/connection is not lost.

I’ve tried Googling for a solution to this issue, but all I’m able to find are countless reports of either people who can’t receive calls at all on their phones (which we can), or people whose phones just generally have bad reception/signal (which ours doesn’t).

I’ve tried toggling basically all the reception/signal/connection-related settings I could find, and the phone has been restarted and switched off/on several times, with no effect.

Is this a known issue that my weak Google-fu is just unable to unearth? And more importantly, is there a solution for it?

  • Have you Erased and Reset the phone to factory settings? – IconDaemon Feb 1 '18 at 15:41
  • @IconDaemon No, not yet. I consider that a last resort, and I wanted to see if there is a less disruptive way of fixing it. – Janus Bahs Jacquet Feb 1 '18 at 16:42

In order of my preference to get things fixed, you'll likely need help from someone else to tell which.

  1. The battery is failing and can't provide the extra power once the call comes in. The radio may be fine at idle listening, but when you call it could need to boost power to get the signal to the tower for transmission from the phone to the tower.
  2. The phone is on an overloaded cell tower and once the call is connected - the cell tower wants to hand off your active call to a less loaded tower that has different distance / signal strength. (The overload would be non-idle lines - towers can handle many devices that are idle - but need to hand off active transmitters and downloaders when bandwidth caps are reached.)
  3. There's something about that specific radio where the tower is cutting the calls short.
  4. All of the above might be summarized as "call the carrier" in question for more help

The battery might be diagnosed by Apple or you might need the carrier to see the transmit power on your phone when this happens. The cell tower shift would also need the carrier to help. I suppose field test mode might work as well to help diagnose this, but I'd start with the carrier first. The last is 100% the carrier that needs to look over the patterns of disconnect. They surely can trace why 5 calls all drop from one piece of gear if you ask.

  • I would never have guessed at the battery issue! The battery generally holds up quite well (considering the age of the phone), about two days of intermittent, light use; but I don’t suppose that means it’s not failing. If it were the second issue, wouldn’t it also be expected to affect our other phones? They are all the same contract, same carrier, some also same model, and some also in the same room. I would expect that under those circumstances, the issue would be expected to appear more or less equally on all the phones, rather than exclusively on one specific phone, wouldn’t it? – Janus Bahs Jacquet Feb 1 '18 at 16:47
  • @JanusBahsJacquet Yes - I would expect it to be evenly spread, but I also know if you can imagine anything possible that could go wrong - in this case - one radio with a bad whatever - it will eventually happen to someone in a shipping product. Apple ships millions upon millions of these and some have to be broken out of the gate no matter how good their testing and manufacturing and self-diagnosis code is. I've added this as reason #3 above in an edit to the main answer. – bmike Feb 1 '18 at 17:39
  • So I called the carrier, and they confirmed that they could find nothing on their end that might be causing it. They suggested switching the SIM card to a different phone to check if it might be the SIM card itself that was faulty—this I did, and it worked fine in the other phone, so presumably not that. They then suggested I try resetting network settings, and this seems (so far so good, knock on wood) to have fixed it. Calling the carrier was something I got from your answer, so if you add on resetting network settings as a fourth option, I'll happily tick this off as the correct answer. :-) – Janus Bahs Jacquet Feb 5 '18 at 15:10
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    @JanusBahsJacquet OK - done. Also - you may make that edit to my posts yourself as well. If ever someone puts in an edit the OP doesn't like - we can always discuss here. In this case, it's a better answer with your suggestion – bmike Feb 5 '18 at 23:18

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