If it is the first time you are using the Voicemail, you should set up or change your default voicemail on iPhone 7 first. If you have set up the voicemail, you can skip to next part. Or else, you can get some helpful information to set up voicemail. As different carriers may have different ways to set up voicemail on iPhone, the part just take AT&T for an example.
Sending a Message. – Lift Handset. – Press Express Msg key or Feature 980. – Enter the mailbox number to send the message to. – To leave your message, press OK or 2. – Record your message at the tone. – To end recording, press OK or #. – To send your message, press SEND or #. Checking Voicemail from an Outside Line.

The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.
If you don’t have access to your online account, you can dial in to your voicemail by pressing and holding the ‘1’ key on your phone’s keypad. After your phone connects to the voicemail system, you can access your password settings by pressing ‘*’, followed by the 5 key.