Most cellphone providers make it possible to block the calls from specific numbers, but they don't usually inform the blocked person that's what happened. You may get a hint your number is blocked when you call someone, and the phone always goes directly or almost directly to voicemail. You can try calling the person from another phone line to see if they pick up, but you may be initiating an uncomfortable conversation.
Cellphone Blocking Technology
Most phone companies let you block people from calling you. Some phone companies also automatically block anonymous callers who call without sending caller ID information to your phone. You can block a particular caller, or someone can block your number on most modern smart phones.
On an iPhone, tap the menu button next to a recent caller's number and select "Block this Caller" to block future calls and messages from that number.
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On an Android phone, hold your finger on a caller's number in the recent calls menu and tap to block the number, or go to the "Settings" menu in the "Phone" app and click "Call Blocking" and edit the list of blocked numbers.
Half Ring Then Voicemail
If a phone rings once and then goes to voicemail or rings only briefly, it usually means either that your call is blocked or that the phone is not receiving calls at all. It could be turned off, in airplane mode, or somehow configured not to accept any calls.
If the phone rings five times and then voicemail picks up, it's more likely that the person on the other end simply isn't picking up the call.
You can't definitively know the cause of a phone barely ringing and going to voicemail because neither a phone company nor the phone's operating system provider will tell you if your phone number is blocked.
Checking From Another Number
The easiest way to check if your number is blocked or if a phone is turned off is to call the phone from another number. Use a friend's phone or your work phone. Alternatively, you can get a new number from a digital service like Google Voice, which offers each user an additional number for free, or Burner, which offers throwaway phone numbers.
Before you do so, consider why the person on the other end may have blocked your number and whether it's possible they'd prefer not to receive a call from you. If you have a mutual friend or acquaintance, it may be better to have that person call and inquire on your behalf. You may also prefer to reach out through social media, email or another less immediate medium.