Two Types of Call Rejection
Call rejection falls into two broad categories: "device-level blocking" and "carrier (network-level) blocking." Understanding this distinction is key to knowing whether the caller can tell they have been blocked.
Device-Level Blocking
This uses your smartphone's built-in feature to block specific numbers - iPhone's "Block this Caller" or Android's "Block number." The call still reaches your phone, but the device automatically rejects it. The caller typically hears only a brief ring before being sent to voicemail, or goes directly to voicemail with no ring.
Device-level blocking requires no additional fees since it does not involve the carrier's network. However, it does not work when the phone is off or in airplane mode. See smartphone privacy settings for detailed configuration.
Carrier-Level Blocking
This blocks calls at the network level before they reach your device. NTT Docomo's "Nuisance Call Stop Service," au's "Nuisance Call Blocking Service," and SoftBank's "Number Block" are examples. The call never reaches your phone, and no call history is recorded. The caller hears a carrier-provided announcement.
Carrier-Specific Announcements When Blocked
The wording of each announcement, the monthly fee, and the number of entries a service accepts all depend on the terms of the plan. Treat the descriptions below as general tendencies and check the current conditions with your own provider.
NTT Docomo
Callers hear guidance to the effect that the call to that number cannot be connected. Because this is the guidance used for blocking, a caller who recognizes it can infer they have been blocked. The number of entries the service accepts is capped.
au (KDDI)
Callers hear guidance to the effect that the call cannot be connected at the customer's request. Because the wording points to a decision by the person being called, it makes blocking relatively easy to infer.
SoftBank
SoftBank's "Number Block" lets you choose among several announcements, ranging from wording that clearly signals blocking to neutral guidance that gives no reason at all. Choosing a vague option can make blocking less detectable.
Rakuten Mobile
When using Rakuten Link's blocking feature, the caller hears normal ringing and then sees an indication that the call went unanswered. No carrier announcement plays, making it difficult for the caller to detect blocking.
What "Cannot Be Connected at the Customer's Request" Means
This announcement does not necessarily mean you have been blocked. It is also used for unpaid bill suspensions, voluntary line suspensions, and expired number change notices. To distinguish blocking from line suspension: blocking only affects calls from specific numbers, while line suspension affects all callers. However, testing this by calling from a different number could violate the Anti-Stalking Act, so respect the other person's wishes. See how to handle anonymous calls.
When Blocking Is Detectable
- Carrier-specific announcements: Carrier-level blocking plays the guidance reserved for blocked calls, which informed callers will recognize.
- Very short ringing before voicemail: Device-level blocking may cut the ringing far shorter than usual before voicemail.
- Consistent voicemail timing: If every call goes to voicemail after the same number of rings, blocking may be suspected.
- Calls from other numbers connect: If your number does not connect but another number does, blocking becomes much more likely.
When Blocking Is Undetectable
- Ambiguous announcements: Where a service lets you pick the guidance, a neutral message leaves the reason unclear.
- Device-level blocking with voicemail: Simply going to voicemail can be interpreted as "busy" or "poor signal."
- "Silence Unknown Callers" on iPhone: Calls from numbers outside your contacts go to voicemail without ringing your phone, and the caller's experience matches an ordinary missed call, so blocking is unlikely to be suspected.
Nuisance call blocking methods covers additional defense strategies beyond call rejection.
Landline Call Rejection
NTT's "Nuisance Call Refusal Service" is the standard option for landlines. After receiving a nuisance call, dial "144" to register the number; later calls from it are turned away with guidance saying the call cannot be accepted. The number of entries is capped. Hikari Denwa offers an equivalent option, which NTT East prices at 220 yen per month including tax as of August 2026. Fees and entry limits differ by line type and provider, so check with your own provider. See landline nuisance call settings for details.
How Blocked Callers Can Tell
There is no definitive way to confirm you have been blocked, but these signs may indicate it:
- Extremely few rings: Far less ringing than usual before voicemail.
- Always goes to voicemail: Regardless of time of day.
- Specific carrier announcements: Blocking-specific messages play.
- SMS not delivered: Device-level blocking can cover SMS as well, depending on the settings. A missing "Delivered" label may point to blocking, but poor connectivity produces the same result.
- No response on other platforms: If LINE messages also go unread, the person may be intentionally avoiding contact.
These signs can also result from poor signal, device issues, or being busy. Persistently checking whether someone has blocked you may violate the Anti-Stalking Act. Respect the other person's decision - call rejection is a legitimate privacy protection measure under phone number privacy management.