HTC One M8 Sprint doesn't connect to roaming partners India
In India, The Official partner of Sprint in India are MTS(For CDMA/800) and Bharthi Airtel,Aircel for GSM(900,1800). Since you are using CDMA,MTS(Sprint partner) supports basic 1x data. and MTS will only work when you are in Main cities in India. :(  

http://www.sprint.com/popups/pop-gprsCarriers.html