Verizon because he could not be on the phone and connected to the Internet at the same time. Not sure if that is still true.
This is a complex situation with multiple entities to blame.
**New phones** on VZW network can do simultaneous voice and data ONLY if Advanced Calling is enabled on the phone (android settings) (HD Voice - VoIP) AND the phone is connected to the LTE network. However, if the phone does not have Advanced Calling enabled, it will not be able to do voice and data at the same time***. Also, if the voice call is started with Advanced LTE-VoIP, the call will drop if you transition off the LTE network down to 2G/3G network.
*** **SOME older phones** had two radios - one for 2G/3G and one for LTE. Those phones CAN do simultaneous voice and data on VZW without Advanced Calling since one radio runs on 1x for voice and the other radio LTE for data. However, good luck trying to find the list of phones capable of that, and VZW wants to push everyone onto LTE only.
Blame: VZW for not clearly defining the phone properties/behavior on their network.
Blame: Phone manufacturers for trying to save money by not including a second modem in their designs.
Blame: Government for not mandating an orderly transition of services and coverage.
NOTE: There should be no problem doing simultaneous voice and data on ANY phone if your data is over local WiFi (yet another modem).
Eventually VZW CDMA network will be turned off (2017???) and all voice/data will be over LTE only. Unfortunately LTE-VoIP has significant issues in my opinion, and there are still rural coverage and in-building issues with LTE in a lot of places.
justacog