However, some cellular service providers allow users to access and update their voicemail by calling their own numbers from working landlines or phones on other wireless networks, so users whose accounts include such an option and who have access to alternative service could keep the voicemail greetings updated even when their own mobile phones cannot connect to cellular or internet service.
1. Setting Up a Verizon or Sprint Voicemail: Open your iPhone's Phone app. It's the white phone icon on a green background on the Home screen. Tap "Voicemail".

From the Android Mobile App: Click the More button at the top left of the mobile app. Select Voicemail. Click Folder with Music Icon located at the top of the mobile app. Click the Record button, give the recording a title, and click OK. The system will call your extension. Answer the call and follow the prompts to record your new greeting.
1. Verizon Wireless: Enter *86 (*VM) at the dialer screen on your Verizon mobile device, then press “Call.” This command dials directly into Verizon’s voicemail system.