I don't feel like this is a product recommendation question, more of a "does this tech even exist and is it feasible" question, but if I'm wrong, feel free to give this question the boot.

Context:

Our company has a bunch of traveling employees who access the company's Exchange server via thier iDevices or android phones, but because of the data protection laws in the state where our company is based (and the nature of the data our company works with), a recent security audit found that all mobile devices (laptops, phones, etc) operated by our company need to have all company correspondence and related data encrypted all the time. For laptops, that was easy: BitLocker or TrueCrypt, problem solved. For phones and tablets, however, I'm stumped. Sure, you can put lock screens/passwords on the phones, but the data is still accessible via external extraction, as law enforcement authorities already know.

Question:

Are there any clients for Microsoft Exchange that run on iOS or Android which store local data encrypted? The people using our mobile devices do a lot of their work while offline, so just giving them OWA access with SSL connection security isn't enough. Are there apps/technologies that present an additional login credential prompt to decrypt locally stored data in the app's storage area on the phone? My gut reaction when I started looking into this was "that doesn't sound like something Apple would allow into the App Store", but I've been wrong before...