CKMadridService

CKMadridService is Apple's secret codename for the service used to send iMessages. Available only in iOS 5.

Creating and sending an iMessage with CKMadridService

//Compose a message
CKMessageStandaloneComposition *composition = [CKMessageStandaloneComposition newCompositionForText:@"Test Message"];

//Get a reference to the shared conversation list
CKConversationList *conversationList = [CKConversationList sharedConversationList];

//Get a reference to the shared Madrid Service
CKMadridService *madridService = [CKMadridService sharedMadridService];

NSString *messageRecipient = @"+1234567890"; // This is the phone number or email of the message recipient

//Make a Conversation
CKSubConversation *conversation = [conversationList conversationForGroupID:messageRecipient create:YES service:madridService];

//Create a message
CKMadridMessage *message = [madridService newMessageWithComposition:composition forConversation:conversation];

[madridService sendMessage:message];

[message release];
[composition release];

Note that you are responsible for releasing the message and the composition, but not the conversation.

References

Header: https://github.com/masbog/PrivateFrameworkHeader-iOS-iPhone-5.-/blob/master/ChatKit.framework/CKMadridService.h