Sometimes I think Android is just a zombie operating system that exists to keep Apple out of antitrust court. Like there is some kind if quid pro quo that Google is doing Apple is a favor which Apple returns somehow.
With a couple of different carriers and phones I was never able to get voicemail working with an Android phone, maybe I could do what they say to activate my mailbox but next week I’d hear from people that they’re hearing a message about how “their voice mail hasn’t been set up yet” which is the same message I hear every time any friend of mine with Android doesn’t pick up. When I got an iPhone it was the first cell I had where voicemail worked at all.
Android (or iOS) has nothing to do with voicemail, it's all on the carrier. All "voicemail" is just your carrier redirecting the caller's call to a special number on their end, where an IVR-like system picks it up and processes it. And maybe some added on features depending on the carrier, like SMS or push/app notifications. That's it, there's nothing fancy about voicemail, and all the magic happens on the carrier side.
I've owned several dozens of Android phones over the years and been with multiple carriers, never had an issue with voicemail. And no one should either, because it's got nothing to do with the OS.
I dunno. The iPhone has some kind of "visual voicemail" and must use some kind of API to get access to my mailbox to download and transcribe messages... and my iPhone has gone 6 months without the voicemail getting reset whereas it would happen between 6 days and 6 weeks with every Android I had. Could well be the carrier treats me differently or the phone does something that stops periodic or intermittent resets initiated by the carrier.
With a couple of different carriers and phones I was never able to get voicemail working with an Android phone, maybe I could do what they say to activate my mailbox but next week I’d hear from people that they’re hearing a message about how “their voice mail hasn’t been set up yet” which is the same message I hear every time any friend of mine with Android doesn’t pick up. When I got an iPhone it was the first cell I had where voicemail worked at all.