I am charged like .03 per KB for internet useage while I am in mexico. I didn´t even think about my music folder maybe accessing the net. Does it? I can not find any infor on the subject! They only have forums for how to download and listen. Someone please help! It is a 1.69 per min to even call sprint to ask this question and all of you know that will take longer than it is worth!
As long as the song is already downloaded to the device or micro SD card, it will not use data to play the song. If you are using an application such as pandora, then data would be used. Hope this helps!
There are a couple of very old phones that would access the Internet to play even locally loaded phones. What phone do you have?
Try putting the phone in airplane mode before you leave and try to play a song. It should work. If not, you know it needs data.