Tap “Phone” on your iPhone’s “Home” screen and tap “Voicemail” to access your voice-mail settings. Tap “Greeting” and select “Default” if you wish to use the default greeting for your voice mails. Click “Custom” if you want to create a personalized greeting, and tap “Record” to say your greeting.
Voicemails have been around in one form or another since the beginning telephone communications. This feature still manages to make its way on every smartphone, despite the rate in which technology is evolving. The reason for this is usefulness – you won’t miss any unanswered calls even if your phone is off. The voice messages from your callers will be transferred to your voicemail box and you’ll be able to listen to them at a later date.

Once you have your message, you need to actually record it. The exact process varies depending on whether you’re using a cell phone or office phone, but here’s the basic process: Press the voicemail button, or press and hold 1 on most cell phones. Enter your password. Record your message. Listen to the message you just recorded. Follow the prompts to save your message. Following Up on Voicemail Messages
If Airplane Mode on its own doesn’t work, turn off WiFi or 4G and then try it again. This can also work.