Question Ghost Voicemail on Unactivated Phone

[Windroid 2483]

My father's backup phone (a Conquest F2), which does not have an active Sim card, is getting ghost voicemail from T-Mobile. That is: The phone keeps giving alerts that there's a new voicemail. When we call the "voice mailbox" from that phone, we get a generic message about T-Mobile which seems to have nothing to do with voicemail.

My father's worried about this. He doesn't know what's going on, and thinks there might be some security risk to his phone here. The (unactivated) Sim card is not even a T-Mobile card, it's an Ultra Mobile PayGo card.

 

[SpookDroid]

Voicemail is unfortunately handled mostly on the carrier side, not the phone itself. Has the phone been used with an active SIM at any point? When he gets the voicemail notification, can he long-press it to see which app is triggering it? Is the phone maybe a T-Mobile version unlocked to use other SIMs? Is there an eSIM active, perhaps?

 

[B. Diddy]

Is the voicemail inbox set up in the first place? What exactly is that generic message from T-Mobile?