I've been getting these bizarre texts recently. I honestly thought they were spam messages with malicious payloads (had attachments with no identifying information WHATSOEVER), so I've been ignoring them / deleting them. Today I got one in close proximity to a missed call, had a suspicion and called myself... yup. I had been opted into "premium" voicemail and this is how they were being delivered.
The ONE thing I miss about having an Apple phone, is that Apple actually massively improved how voicemail worked. And it's been over a decade now, and every single "premium" voicemail service that I have been subjected to since then that isn't that, is objectively inferior to a carrier's baseline voicemail service. Like... come on?!?!