Apple never released its instant messaging service iMessage on Android phones because it is a reason for people to use an iPhone.
This is evident from statements and emails from Apple employees
maker Epic Games as part of a lawsuit against Apple (PDF).
Epic says Apple is consciously tying customers to its ecosystem of devices and iMessage is an important part of making that happen.
Epic filed a lawsuit last year after the company put its own payment system in
Apple then removed the game from the App Store because Epic violated the platform's rules.
To support the argument that Apple is monopolizing the market, statements and emails from Apple executives are cited by Epic in the lawsuit.
"The main reason it's hard to leave Apple is iMessage," a former Apple employee wrote in an email.
"iMessage thus contributes to a serious containment."
Apple software boss Eddy Cue responded that "bringing iMessage to Android would do us more harm than good".
Apple CEO Craig Federighi also said iMessage on Android would not benefit the company.
"It would remove an obstacle for families with iPhones to give children an Android phone."
Apple released iMessage along with iOS 5 in 2011.
Two years later, Apple would have made the decision not to make an Android version.
With iMessage people can send messages and images to each other via the internet.
There are therefore no SMS costs associated with this.
However, if an Apple user sends an iMessage to an Android owner, they will receive the message as a text message.