How to Check iPhone Voicemail From a Landline
If you are outside of your mobile carrier's network or you do not have access to your iPhone, you can still check your voicemail. The voicemail system is accessible from a landline phone. When you access your voicemail, you can manage voice messages as you normally would if you were calling from your iPhone. Depending on your mobile carrier, you may incur charges for accessing your iPhone voicemail from a landline phone.
Dial your iPhone 10-digit mobile phone number from your landline phone.
Listen for the greeting and press "*" when it begins to play. Depending on your carrier, you may need to press "#" instead.
Enter your iPhone voicemail passcode when prompted.
Review your voicemail messages by following the voicemail system prompts and hang up your landline phone when finished.