Comment by otterley

Subaru has published a Technical Service Bulletin that appears to offer a free firmware update to switch the Starlink system to use VoLTE. Affected vehicles are:

2016-18MY Legacy/Outback 2016-18MY Impreza 2016-18MY Crosstrek 2016-18MY Forester 2017-18MY WRX

See https://static.nhtsa.gov/odi/tsbs/2021/MC-10189606-0001.pdf for details. And, yes, Subaru is reimbursing dealers for this work.