A:AnswerThe Series 4 watch can read both your heart rhythm (EKG) as well as track your heart rate. The cellular data is only needed if you want/need access to your text messaging and music streaming without your iphone nearby (within Bluetooth range). The cellular data isn't needed for heart monitoring. I have the GPS only version and I am able to access both of these functions with or without my iPhone nearby.
A:AnswerYes, you can pair this with an Apple Phone on the Sprint network. You do not need to buy the watch from Sprint nor deal with them in anyway for the Wi-Fi version of the Apple Watch. If you buy the cellular version and wish to use the cellular features, you will need to have that registered with your cellular provider.