Authorize.net for mobile phones is designed for a card present environment, where you have someone take payment at a front desk or at the customer's table, and there's limited number of known devices doing the charging. It's not designed for large-scale app payments, where the security scope is much larger. You can of course cheat and have your app use SSL protocols to interact with a web site that actually does the charging, in which case you can just use AIM. It's nominally against the rules, but assuming your app is well-programmed, the weak point is the web site, and you're no worse off than anyone doing web-based charging using AIM. Basically, you might get charged an extra monthly fee for not passing automated security scans, but that's probably about it.
Of course, I don't work for Authorize.net and you can't necessarily take this as a definitive answer. But I do know there's no way to automate mobile approval - that would defeat the whole purpose of having it in the first place.
