Can't call out and messages are not left on voicemail

When your iPhone is locked (the screen is off), Do Not Disturb silences all incoming calls, text message notifications, and alerts on your iPhone. Unlike silent mode, Do Not Disturb sends incoming calls straight to voicemail.
https://www.payetteforward.com/why-does-my-iphone-go-straight-to-voicemail-heres-the-fix/

You apparently have unheard messages on the voicemail system provided by your telephone company. This system records messages when someone calls while you're already on the phone. Please contact your telephone company for instructions on accessing their voicemail system.

You have unheard messages on the voicemail system provided by your telephone company. This system records messages when someone calls while you're already on the phone. Please contact your telephone company for instructions on accessing their voicemail system.

As for incoming calls, are they possibly going to the aforementioned voicemail system?"

You have unheard messages on the voicemail system provided by your telephone company. This system records messages when someone calls while you're already on the phone. Please contact your telephone company for instructions on accessing their voicemail system.

As for incoming calls, are they possibly going to the aforementioned voicemail system?

Call services From your phone, you'll be able to access and change the settings of various call services for your phone.Contact your mobile operator to find out about the availability of call services. From the Home screen, press MENU and then tap Settings > Call. Fixed Dialing Numbers Restrict outgoing calls to a fixed set of numbers. To enable this feature, you must know your SIM card's PIN2 code.
Voicemail service Shows the current voicemail service being used.
Voicemail settings Specify another voicemail number aside from the voice mail number on your SIM card.
Clear voicemail notification If you have a notification of a new voicemail, you can clear the notification with this option.
TTY mode Enable this mode to connect and use a compatible TTY device with the phone.
Hearing aids Enable HAC (Hearing Aid Compatible) to amplify in-call volume.
Phone settings Edit the call reject message, choose whether to open the message editor when you reject a call with a message, and choose whether to allow automatic saving of an unknown contact number when a call with that number ends.
Cell broadcast Enable or disable receipt of cell broadcast messages from your service provider.
Cell broadcast settings Configure channels and language for cell broadcast messages.
Call forwarding Select how you want your phone to handle busy, unanswered, and unreachable calls. You can also set the call forwarding option for all incoming calls. Call barring settings Choose whether to block various categories of incoming and outgoing call.
Additional settings Enable or disable operator services such as caller ID and call waiting.

Answering a call:

When a call is received the phone rings and displays the caller's
phone number, or name if stored in the Address Book.
1. At the incoming call screen:
• Touch and slide to the right to answer the call.
• Touch and slide to the left to reject the call and send it to
your voicemail.
• Touch and slide the Reject call with message tab upward and tap
a predefined text message to send to the caller.
- I'm driving
- In a cinema
- I'm in class now
- I'm in a meeting
- Sorry, I'll call later
- or -
- Tap Create new message to compose a new message.

You may also click on this link to download the user manual for complete instructions with photos:

http://www.samsung.com/us/support/downloads/SGH-I897ZKAATT

Note:
"Answering a Call" portions is on Page 46

to change txt message tone:
go to text message main screen then press the top left button.scroll down to settings and click. then scroll down and ull see "new message alert" and there u go.
to the same for picture messaging.
ring tone:
go to phone
click the top left button
scroll down to settings, then general
scroll down the incoming call. and clik on that and u will have options

Probably not, but the voice mail extension is still a dialable number. Try 500 or 165 or asking whoever installed it what the extension is.

It will prompt you the same as if you had pressed the MESSAGE button, only there will not be any new messages. You just have to play the OLD messages and you'll hear them.


Carl