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 one 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
NTT Docomo
Callers hear: "The call to this number cannot be connected." This is a blocking-specific message, so Docomo users who recognize it can infer they have been blocked. The service is free and supports up to 30 numbers.
au (KDDI)
Callers hear: "The call to this number cannot be connected at the customer's request." The phrase "at the customer's request" makes it relatively clear that the call has been blocked. The service costs 110 yen per month.
SoftBank
SoftBank's "Number Block" (110 yen/month) offers 9 different announcements to choose from, including vague options like "This call cannot be connected" that do not clearly indicate blocking. Choosing the right message can make blocking less detectable.
Rakuten Mobile
When using Rakuten Link's blocking feature, the caller hears normal ringing followed by "The call was not answered." 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: Docomo and au use blocking-specific wording that informed callers will recognize.
- Single ring before voicemail: Device-level blocking may produce just one ring before voicemail, compared to the normal 4-6 rings.
- 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 is confirmed.
When Blocking Is Undetectable
- SoftBank's ambiguous announcements: Choosing a vague message like "This call cannot be connected" makes 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: The caller hears normal ringing, so they are unlikely to suspect blocking.
Nuisance call blocking methods covers additional defense strategies beyond call rejection.
Landline Call Rejection
NTT's "Nuisance Call Refusal Service" (660 yen/month) is the standard option for landlines. After receiving a nuisance call, dial "144" to register the number. Subsequent calls from that number hear "This call cannot be accepted." Up to 30 numbers can be registered. A call-blocking phone offers automatic warning messages in addition to blocking. 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: One ring instead of the normal 4-6 before voicemail.
- Always goes to voicemail: Regardless of time of day.
- Specific carrier announcements: Blocking-specific messages play.
- SMS not delivered: On iPhone, device-level blocking also blocks SMS. If "Delivered" does not appear, blocking is possible.
- 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.