In context: Apple's services purposefully lock consumers into the iPhone ecosystem, preventing them from making an easy switch from iOS to Android, and iMessage is among the top culprits for this. At least, that's according to an Epic Games court filing, which cites information from several of Apple's top-ranking executives.

While the Epic vs. Apple case centers on the App Store's controversial 30-percent commission on in-app purchases, new filings published ahead of next month's trial shed more light on some of the companies' primary arguments against one another.

Epic argues that Apple purposefully designed its services to lock consumers into the iOS ecosystem, preventing them from easily leaving. While some services, like Apple Music, are available cross-platform, iMessage has long been Apple-only.

Epic's filing alleges one unnamed former employee said in an email, "The #1 most difficult [reason] to leave the Apple universe app is iMessage ... iMessage amounts to serious lock-in." Following the email, Apple's Phil Schiller responded: "moving iMessage to Android will hurt us more than help us, this email illustrates why."

Meanwhile, Craig Federighi, senior VP of Software Engineering, is quoted in the filing as saying, "iMessage on Android would simply serve to remove [an] obstacle to iPhone families giving their kids Android phones."

The filing also claims that as early as 2013, senior vice president of Internet Software and Services Eddy Cue made the decision not to develop a version of iMessage for Android, even though such a version was, in theory, possible.

As well as iMessage, Epic's filing cites FaceTime as another example of an Apple lock-in service. Apple's Tim Cook, Craig Federighi, and Phil Schiller, along with Epic Games CEO Tim Sweeney, are all expected to take to the stand next month when the trial begins. It'll be interesting to see how this one plays out.