IPhone 5s and All Models Support VoLTE 5, 5s, 6, 6 Plus
Hey there,
The iphone Fives is delivering a qualcomm LTE chipsed: Qualcomm MDM9615M LTE Modem (evidence: https://fr.ifixit.com/Teardown/iPhone+5s+Teardown/17383).
As stated right here on the main maker web site: https://www.qualcomm.com/products/gobi/modems/specs.
The Qualcomm MDM9615M supports VoLte.
The iphone 5s SUPPORTS VoLTE, because its equipment supports this method.
As we see on apple ios 9.2 upgrade, they do not want to allow it on the baseband for obvious marketing reasons!
https://fr.ifixit.com/Teardown/iPhone+5s+Teardown/17383.
http://www.tmonews.com/2014/05/iphone-can-support-volte-but-likely-wont/.