It is a Sprint limitation. Older Sprint phones can do voice and data but the newer Sprint "Spark" enabled phones cannot do voice & data unless they are on a VoLTE call. This is due to the Sprint model only have one radio so it can only do voice... or data. Verizon (and Sprint used to in non-spark phones) puts two radios in so they can have one use the phone .. and the other uses data. That way they can avoid this limitation. Even though Verizon does have VoLTE launched they still are making phones this way for now so .. Voice & Data will work for Verizon. It will for Sprint too ... on wifi .. or once they roll out VoLTE
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As for AT&T and T-Mobile they operate on GSM mainly so they can do Voice and Data with one radio ... regardless if it is a VoLTE call or not. A VoLTE call for AT&T and T-Mobile just means you get to hold LTE and stay on the call instead of dropping from LTE to HSPA.