This is definetly the T-Mobile Voice Mail processing system.
It is possible that the calls you receive from this number are people checking their messages and using a call-back feature to directly dial the number from the automated system.
I got a voicemail today. It's creepy that the recorded voice mail was a baby screaming and it sounded like my daughter and my sister trying to calm her down.
Caller leaves a voice-mail asking for a return call at 888-560-0054, with an extension. If I try to block 805-637-7243, my call blocker says I'm blocking voice-mail. This company, claiming to be a debt collector, is in violation of several federal and state laws and regulations for using the T-Mobile voice-mail line (obviously cloned) for their in-bound calls.