VZW testing Voice over LTE aka VoLTE. Iphone 5 can do VoLTE according to Qualcomm.

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Vizin said:

In theory any phone could do VoLTE with the proper software update. VoLTE is basically voice over IP, it uses the phone's data connection instead of a separate voice network. It would just be integrated into the phone's OS - you'd use the normal calling function instead of a special app, you'd use your regular phone number, and presumably it'd be billed as voice minutes instead of regular data usage.

One thing that interests me about VoLTE is there's no reason it couldn't be used over a regular Internet connection, meaning we might be able to make calls over WiFi without having to use a network extender. I get no service in my house so I have a network extender for calls and SMS, but it's really flakey and I wish I could just use WiFi. (We'll see if the carriers end up allowing this.)

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No reason they wouldn't allow it once they get everyone on unlimited talk plans

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Get ready for tons of dropped calls. VoLTE is all or none.

One of reasons Verizon was " presumed" to have less dropped calls was CDMA's superior handling of voice compared to ATT's WCDMA voice calls.

If network is overloaded on WCDMA voice call with drop.

Similar thing will happen to VoLTE calls. Verizon knows it.

Vizin said:

Well, I've always had a sneaking suspicion that Verizon/AT&T haven't worked on adding WiFi calling (like T-Mobile) because they want to sell more microcells. (Or they just don't want to admit their service doesn't work everywhere.)

With VoLTE it's a lot less technically challenging to enable WiFi calling - the bulk of the work has already been done (Developing a VoIP system), they just need to make it accessible from the open Internet, which is mostly an issue of authentication.

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For whatever reasons, maybe their whole "network" thing, neither has done wifi calling. VoLTE doesn't make it much easier, and we know, at least in AT&T's case on GSM/UMTS, that UMA and it's software-based descendent that T-Mobile now uses, that wifi calling is already very practical.

VoLTE is not simply VoIP

Actually, Vizin, VoLTE is not simply VoIP. It requires support from the lower layers to improve voice performance and prioritise the voice traffic.

"plain" VoIP would not offer the same user experience and will be more prone to call drops, particularly at the cell edge, than VoLTE.

For the above reason, there is a difference between saying that a mobile supports VoIP and that the same mobile supports VoLTE. While all smart phones support VoIP not that many support VoLTE, at the moment.

It is very likely that mobile operators will not allow non-VoLTE terminals to make and receive calls on the mobile number provided by the operator, using VoIP over LTE. It would be difficult to guarrantee the quality of the call. Instead, they will probably use CSFB for these users. After all, over time there will be increasingly more spare capacity on 2G and 3G.

Having said that, a VoLTE phone could offer superior performance also for other VoIP services, not necessarily offered by the mobile operator. For that, however, the mobile operator should trust the QoS settings of the VoIP stream and offer the same QoS with VoLTE (QCI 1). In practice, however, I doubt mobile operators will accept to do that and there are many arguments why they wouldn't.