Both phones need to be VoLTE enabled phone side and carrier enabled on the current tower they are connected to for a VoLTE call to take place.
They need a mutual handshake. Forcing the 950/XL through on Block C fails for users unless every handset and tower in the US is VoLTE enabled to channel the call, yes?
How do you use VoLTE when calling a landline? Or Grandma's flip phone?
Verizon starts rolling out VoLTE, but on only 2 phones to start - FierceWireless
Yes you are correct. That was something I stated a number of posts ago. Advanced Calling only works with other Advanced Calling enabled phones. Verizon has several now, but there are thousands, if not 10s of thousands of customers either using a non Advanced Calling enabled or capable handset. My mother-in-law is one of them.
Of the 59 handsets that Verizon offers, 40 of them are Advanced Calling capable, none of them basic flip phones (not everybody wants or can afford a smartphone). That means if they allowed the 950/950XL on it's network as VoLTE only, it would not be able to communicate with 1/3 of the handsets it offers (that is a lot of people). That defeats the purpose of what Verizon provides, the ability for a Verizon customer to fully use its network to communicate. Furthermore, just because an area has LTE coverage, doesn't mean you get LTE everywhere in that area. There are LTE dead spots within those areas. If you get into one of those dead spots, you lose ALL communication, because Verizon uses CDMA as it's 3G voice/SMS.
Until Verizon dumps its CDMA network (which it is in the process of doing), phones like the 950/950XL will not work.
I really wish people would stop and think. Verizon has millions of customers and it has to be able to provide its services to EVERYONE of those customers. Even though Verizon values ALL of its customers (and it does contrary to the rants you read in this and other forums), it's NOT going to offer a device that appeals to a small fraction of its customer base and is unable to communicate with EVERYONE of its customers.