Thanks for the explanation. It does indeed sound like there’s no convenient solution till your whole system gets revamped. To briefly explain *why* I don’t want your voicemail enabled: I use my USMobile number as a forwarding line for Google Voice. Google Voice’s voicemail is frankly superior to yours so I want to use it exclusively. When your voicemail kicks in it interferes with Google Voice’s operation, causing me frustration and a real mess. I’ll give some thought to whether I want to be bothered with going through a quarterly exercise of calling and re-disabling your voicemail.
To set up Visual Voicemail, tap Set Up Now. You’ll be prompted to enter and confirm a voicemail password. Next, you’ll have the option to choose the default voicemail greeting or record your own. If you want to record your own custom greeting, tap Custom. Once you’ve entered created your password and chosen your greeting, you’ll be able to receive voicemails and view them in the Phone app.

Yeastar S-Series VoIP PBX integrates a free voicemail system. Voicemail is a modern kind of answering machine that allows the callers to leave audio messages in case of unavailability.
How to Record Voicemail Greeting on iPhone Tap the Phone app to open it. Tap the Voicemail tab. In the Voicemail screen, tap Greeting . In the Greeting screen, tap Custom. This is where you'll record your voicemail greeting and stop using the default... Tap Record and start speaking. When you're done recording the voicemail greeting, tap Stop . See More....