There are a few main reasons why an incoming call may go straight to voicemail without ringing your phone:
Your phone is turned off or has run out of battery
If your phone is turned completely off or the battery has died, incoming calls will be directed to voicemail instead of ringing. This is because the network recognizes your phone can’t receive calls at the moment.
You have no network coverage
If you are in an area with weak, limited, or no network coverage, calls will go to voicemail. This includes places like basements, elevators, thick-walled buildings, remote rural areas, or even traveling abroad in some cases. The network can’t connect the call properly due to the lack of signal.
You have enabled Do Not Disturb
Many smartphones have a Do Not Disturb or DND mode that can be enabled to block calls and send them directly to voicemail. This is useful if you are busy, sleeping, in a meeting, or simply don’t want to be disturbed by calls.
You have call forwarding enabled
Call forwarding allows you to redirect incoming calls to another number, such as your voicemail box or another phone line. If you have call forwarding enabled, all calls will go straight to the forwarded destination without first ringing your phone.
You are on another call
If you are already occupied on a phone call, most networks are configured to send a new incoming call directly to your voicemail. This prevents the caller from interrupting your current call and allows them to leave a message.
Network congestion or glitches
In rare cases, network congestion or technical issues can sometimes result in calls going straight to voicemail. This is not common but can happen if the network has an outage or experiences high traffic loads.
You have blocked or ignored the caller
On smartphones, you usually have the option to block specific phone numbers, which routes their calls to voicemail automatically. You can also ignore calls from certain contacts, sending them straight to voicemail.
Caller has an anonymous blocked number
If the incoming call is from a blocked or anonymous number, some providers will send it directly to voicemail. This prevents unwanted calls from ringing through to you.
You have a SIM card error
Sometimes SIM card errors or malfunctions can occur that prevent your phone from receiving calls properly. This typically results in the call defaulting to voicemail instead of ringing on your end. Resetting the SIM card usually resolves this.
Your voicemail box is full
A full or overloaded voicemail box can also result in calls going straight to a fast busy signal instead of ringing your phone. This indicates there is no space left to accept new messages.
You have a feature like Find My iPhone enabled
On iPhones, having Find My iPhone enabled sends calls straight to voicemail when the device is reported as lost. This prevents someone who finds your phone from answering calls.
An app or setting is disrupting your calls
Some third party apps can disrupt your normal call handling and routing if granted certain permissions. Check settings and app permissions to disable anything that may be redirecting your calls.
Your phone line has call screening enabled
Some phone providers allow you to enable call screening features that ask callers to announce themselves before the call rings through to you. The call goes to voicemail if the caller hangs up.
You have a new phone number
If you have recently changed your phone number but not updated it everywhere, calls to your old number will now be going to someone else’s voicemail or a disconnected message.
Conclusion
In summary, the main reasons calls can go straight to voicemail include having your phone switched off, no network coverage, call forwarding or blocking enabled, Do Not Disturb mode activated, your voicemail box being full, or the caller having an anonymous blocked number. Less common causes include SIM card errors, network glitches, call screening features, and having certain apps or settings enabled that send calls to voicemail.