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I'm on iOS 10.2.1. For me the problem started after I erased my phone and restored a backup. This morning was the first time I've had transcription work in over 6 weeks.

Did you turn you left phone off and on before testing? It didn't work for me until I did that.
Yes I did a hard reset. But I am on PB 10.3. I have to wait until Apple releases 10.3 to the public before Apple can do anything to fix it.
 
Mine is back working correctly. Even Voicemails from a couple days ago. I'm on 10.3, Beta 7
 
Mine started working again on its own a couple of days ago too. Didn't have to do anything. Apple must have flipped some switch on their side.

iPhone 7 / iOS 10.3b7 / T-Mobile
 
All my old voicemails transcribed. I don't know if it happened before or after I upgrade to iOS 10.3 since I checked a few hours after upgrading to iOS 10.3. The old voicemails had not transcribed after new ones started transcribing. I last checked a few days ago so it may have been iOS 10.3.
 
Mine are still not working! Did anyone have to restore to factory settings? Apple is having me restore to new phone before they will elevate it to the engineers.
 
I didn’t even switch carriers. I’ve had sprint for years and just got a new phone a few weeks ago, and now I can’t get voicemail transcribing. Any new tips?
 
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