What I meant was my android phone regularly downloads mp3s, and it seems the problem lies elsewhere. I don't have an iphone, and I don't understand the rest of your request. The problem I am experiencing seems to happen with some, but not all phones.
For anyone who would like to help, I've created a test version of this problem using AbanteCart v1.2.14
With a mobile device visit appalachianmusic.net/cart
There is a test customer account, follow login instructions and attempt to download the music file
This works on some phones, but not all. seems to always work on pcs fine. would appreciate hearing from anyone with results