I'm considering returning my S5 because it can't do this. The only phone I'd consider going to is the Nexus 5 bought through Google because I hate all of the Sprint bloatware.
Both Galaxy S5's and Nexus 5's will work on 3G and LTE. There must be an issue in your area which is giving you problems.
That's not the question. The question is- can you talk on the phone while also using data over LTE/3G?
This is for the S5, but I assume it would work on the galaxy note 4 and all other devices with this issue. I wanted to let you know that there is a very easy work around for this limitation. It is supplied by Google Inc through the Hangouts Dialer app. I'm not sure whether or not you need Hangouts installed to use it, but it allows you to make calls via the data network and still use the network to browse the web, etc. I have tried it several times at home with WiFi off and it works flawlessly so far. It's sad that Sprint didn't find a way to bypass this limitation on their own, or at least inform customers, but this is an easy and seamless solution by Google. I put the icon right next to my default phone icon for future use. Additionally, I can not believe that Sprint is not aware of this work around. I spoke to a few different representatives today, and none were able to offer a solution. I found this on my own searching the play store. Hope this helps!!