I’m looking for some advice before embarking on the development of an app.

Here’s a bit of background.... we have a website which sells MP3s. It’s our own music and our MP3s are currently only sold via our site, which customers download (or order on CD) and save on their computer. We want to continue selling them exclusively via our website and not on iTunes.

The problem is that many customers are now using smart phones and tablets to download the files. It is fine if they save onto a computer then sync with iTunes (or similar software), but more and more people are doing it directly with their devices. We’re constantly asked questions like “why does it only play for 30 seconds and then skips back to the beginning?” The answer is that they’re streaming the audio on their mobile device, which doesn’t allow them to save by default (I know this is the case with Apple. I’m unsure about other devices).

At the moment we recommend a third party app, which allows people to save directly onto their iPhone / iPad. It works well and solves the above problem. However, I’d like to create an app for our website that has this function – in addition to some basic functions, such as the ability to browse our products, view our blog, etc. But the main purpose is for the user to be able to save our downloads and store them in one place, within the app.

Is a download manager function difficult to program?

I know Apple do not allow files from websites (such as MP3s, PDFs, etc) to be saved onto the device by default.
What about other operating systems, such as Android, Blackberry and Windows 8 phones? Does anyone know if they allow files to be saved?

Is it better to find an app developer who can build an app to work on all operating systems or start with iOS, then find someone else for Android, etc?

Thanks in advance.