All my outgoing calls keep on dropping/call ended. Please help

Try these steps:

1. Restart your device.
2. Try to reset your device. This won't delete your data stored on it.

• Press and hold the Sleep/Wake button
• Press and hold on the Home button
• Keep holding both buttons until the display turns off and back on with Apple logo on it.

If this does not help, restore your device to factory settings. Note that this will erase the data from your device.

Take a look this Apple Support article: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support.

Alternatively, you may go to Settings - General - Reset - Reset All Settings

https://support.apple.com/en-us/HT201559

If these steps don't work, contact Apple and ask for help.

https://www.apple.com/support/iphone/contact/

You are welcome. You can also contact your carrier support, maybe there're some problems with network in your area or something like that.

I also had this issue with my iPhone 4S running 8.4. My phone was ending calls before dialing out after I Reset All Settings (General / Reset / Reset All Settings). I attempted to restore my backup, but it still had the same problem. After contacting my carrier Sprint via chat and they instructed me to dial ##873283#, which is a service update and then now it is able to dial out.