You can use voice and data simultaneously as long as you're getting LTE service at the time.
Right and Wrong. You get VoLTE at the same time as long as:
1. You and the other person are on the same cell network (Verizon to Verizon works, Verizon to T-Mobile will not work)
2. You AND that other person both have LTE coverage (otherwise it's a CDMA call, with all the traditional limitations)
3. Neither of you leave LTE coverage (the call will drop)
4. You both have the [free] feature enabled in your Account and on your Devices
If any one person doesn't meet all of that, then you won't get SV&D. Simply being in LTE coverage and having it turned in does not mean it will work. The person you are calling is also a point of failure for getting that capability to work.
Android phones are using a different setup than Apple to get it to work on Verizon. On those devices, you certainly get SV&D.
VoLTE is currently not compatible across carriers, so unless you always call people on the same carrier you use, you pretty much shouldn't even consider this device to have this capability, cause you will not have it a lot more often than you do. You certainly won't have it if you call anything that *isn't* a cell phone (or something like a Skype Number). You can, however, use something like Skype to skirt around the device's deficiency in this area (since it will place any call you use it for over the data connection)...