Unable to make a call after updating iPhone to iOS 18.4.1

The "Call Failed" issue typically applies to outgoing calls because it occurs when your phone attempts to establish a connection to the network and initiate a call. Incoming calls, on the other hand, are reliant on the network's ability to route the call to your phone, which is a different process.

It seems your iPhone is experiencing call connectivity problems, causing calls to abruptly end with "Call Back" or "Cancel" options on the screen, refer to the pics below. This happens when a call is failed which you forgot to mention in your post.

If you are experiencing intermittent silence or drop or the call itself is disconnected during voice calls on your iPhone, there are a few things you can try to fix the issue:

1. Poor signal strength can cause dropouts or silence during a call. Try moving to an area with better reception or switching to a different network if possible.
2. Restart your iPhone --> Restart your iPhone, iPad, or iPod touch - Apple Support
3. Force Restart your iPhone --> Force restart iPhone - Apple Support)
4. This may help too. General Troubleshooting iPhone Issues: St… - Apple Community
5. Check if your audio is not connected to external Bluetooth speakers.
6. Few other reasons why your device keeps Muting / Dropping / Disconnecting Calls or encountering Call Failed.
   1. Your device's cellular signal Is weak.
   2. It's Raining (Cats & Dogs) in your area or in the area where your device is hooked.
   3. The Cell Tower is Overloaded / Heavy Traffic (Telecommunication)
   4. You've misunderstood your signal strength
   5. You are moving and the signal weakens while changing from one tower to another
7. Other culprits may include the following:
   1. Bad Weather: Precipitation can leak into phone cable lines and cause disruptions. Lightening, even at a distance, can disrupt the connection.
   2. Wireless interference: Power lines, radio, or television. transmitters, transformers, and other electronic devices may cause noise on the phone line. --> Resolve Wi-Fi and Bluetooth issues caused by wireless ...
   3. DSL services: The high-frequency signals coming from DSL (digital subscriber line) devices sharing the phone line can create problems for other technology connected to the line.
8. Try to turn on Airplane mode, wait for 10-15 secs, and turn off aeroplane mode.
9. Check the health of your device's Battery. Change if below 80%
10. Take the SIM out and Put it back again, Change your SIM, if it is damaged
11. Time to contact your Carrier / Change if required

What Call? On an iPhone, you can make and receive various types of calls. Here are the different types:

1. These are standard voice calls made over the cellular network. They utilize your carrier's voice network to connect you with other phone numbers. Allow phone calls on your iPad, iPod touch, and Mac
2. FaceTime Audio allows you to make voice calls over Wi-Fi or cellular data using your internet connection. It provides higher audio quality compared to traditional cellular calls.
3. FaceTime Video enables you to have video calls with other FaceTime users. It uses the front or rear camera on your iPhone to transmit live video during the call. Use FaceTime with your iPhone or iPad - Apple Support (IN)
4. VoIP (Voice over Internet Protocol) calls use internet connectivity to make phone calls. Apps like Skype, WhatsApp, Viber, and Google Hangouts utilize this technology, allowing you to make voice and video calls over the Internet.
5. Some carriers support Wi-Fi calling, which allows you to make and receive calls over a Wi-Fi network instead of relying solely on cellular coverage. This can be useful in areas with weak cellular reception. Make a call with Wi-Fi Calling - Apple Support (IN)
6. The App Store offers numerous calling apps that utilize different technologies. These apps can provide additional features and options for making calls, such as international calling, call recording, and more.

It's important to note that the availability of certain call types may depend on your iPhone model, iOS version, and carrier.

It's not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

Was/Is your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...