Membership App Shopping Cart Software

Hi,
I'm working on team that's building a mobile device-based application that will have a monthly membership fee. We're basically trying to find a type of shopping cart back-end that we can integrate with the rest of the application (there's a web-based component of the mobile app) that can include a user portal, recurring monthly payments, an accounting back-end, etc. and, ideally, we can use to ensure that when someone logs in (via mobile device usually) their membership is active.

Does anyone know of any good solutions for this that will be integrate-able with our broader application and is a rather robust solution out of the box (we know there will, of course, be some development necessary)? I've looked at osCommerce and number of other commercial products but haven't really found much that is in line with what we're looking for.

Thanks!

You'll probably have to roll your own...