A new iPhone that cannot hold a call is alarming, but the cause is usually mundane: the line did not finish provisioning, the carrier settings never updated, or an eSIM transfer half-completed. Hardware faults exist and do happen, but they are the last thing to suspect, not the first. Here is the order to work through — cheapest and fastest first — and the point at which the problem stops being yours to fix.
Step 1: The five-minute checks
- Restart the phone. Genuinely — a large share of post-transfer cellular faults clear here and nowhere else.
- Check for a carrier settings update: Settings, General, About. Wait on that screen for fifteen seconds; if an update exists, a prompt appears.
- Check for an iOS update. Launch-window cellular bugs are common and usually fixed in the first point release.
- Toggle Airplane Mode on, wait ten seconds, off. This forces a fresh network registration.
- Confirm the line is actually enabled: Settings, Cellular. A transferred eSIM can appear present but be switched off.
Step 2: If it says No Service or SOS after a transfer
This is the most common single complaint after an upgrade, and it is an eSIM provisioning problem far more often than a signal problem. The old device's line was released but the new one never completed activation, so the phone has no credential to register with.
- Open Settings, Cellular and look for a line marked as needing activation — tap it and follow the prompt.
- If the line is missing entirely, the carrier has to re-issue the eSIM. This cannot be fixed from the handset.
- Do not factory reset to solve this. It does not restore a released eSIM and costs you an hour.
- If the old phone still has the line active, keep it powered on until the new one works — it is your fallback.
Step 3: If 5G is missing
- Check Settings, Cellular, Cellular Data Options, Voice & Data — 5G On or 5G Auto must be selected.
- Confirm your plan includes the 5G tier you expect. Some prepaid and entry plans are limited to a slower 5G layer, and no setting overrides that.
- Low Data Mode and Low Power Mode both restrict network behaviour. Turn them off while testing.
- Remember that MVNO lines can be deprioritised on a busy tower, which looks exactly like a slow connection and is not a fault.
Step 4: If calls drop but data works
That pattern points at voice provisioning rather than radio hardware. Check that Wi-Fi Calling and VoLTE are both enabled — on modern networks, voice runs over the data network, and a line provisioned without VoLTE will drop calls while data behaves perfectly. Both settings live under Settings, Cellular. If VoLTE is missing as an option entirely, the line needs a carrier-side fix.
Before you visit a store
- Note whether the problem follows the line or the phone — put the eSIM on another device if you can. This single test tells the technician more than any description.
- Record when and where it happens. Intermittent faults are diagnosed from patterns.
- Check your return and exchange window and stay inside it.
- Back up before any appointment; a store's first move may be a restore.
Jean Gilles has researched personal finance, consumer technology, and wireless pricing for over a decade. He founded ShopCellPlans in 2019 and writes every review on the site.
Frequently asked questions
Why does my new iPhone say No Service after transferring from my old one? +
Will a factory reset fix cellular problems? +
Why is my iPhone on 5G but slow? +
Calls drop but data is fine — what is that? +
How do I know if it is the phone or the network? +
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