iOS (the iPhone operating system) uses a system similar to Trash on a Mac, in that deleting a voicemail will remove it from view but not necessarily remove the file completely. If your iPhone is still picking up that file, it will show as not being able to be deleted.
Recent trends in voicemail have leaned towards the desire for many individuals to relate on other forms of digital message than traditional voice mails. More individuals have not set up their voice message nor return calls in a decent amount of time. However, some voice messages even steer individuals to contact by email for a quicker response. If you still enjoy the concept and position that a voicemail box serves, you may feel compelled to add a witty voicemail greeting to your caller. The following selection has been shared by others around the global and intended to inspire you to create your own unique humorous voicemail.

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
When you're in a call, wait for the Add Call button to light up, so you can add a third caller via 3-way calling. Tell the other person to wait, click the button, and call yourself. Stay on the line and listen to your own voice mail greeting, then for the tone that indicates recording has begun. Tap Merge Calls. All three calls are merged—and the third one (your voice mail) is taping the other two.