Not sure if this is something I just noticed or something that happened with the upgrade to iOS 9, but it appears that there are some issues with landline users leaving voicemail on my iPhone 6. If you haven't already, see if this occurs on any of your phones. Take an iPhone 6 that has been upgraded to iOS 9 (13A344) and call it from an AT&T landline. If LTE Voice + Data is enabled, I receive dead air where there should be a greeting. The voicemail system still records after the greeting has finished, but all you hear is silence during what should be my greeting. Disabling LTE Voice and only enabling LTE Data, the greeting is heard on the landline caller's end. This does not seem to occur if calling from another AT&T wireless number or from a variety of VoIP providers. This has to be a POTS line (and may not need to be specifically AT&T provided either). Edit: Occurs only on iPhone 6 and newer and on iOS 8.4.1, not just iOS 9.