Here is a tutorial which does exactly what you are looking for: the MFMessageComposeViewController.
http://blog.mugunthkumar.com/coding/iphone-tutorial-how-to-send-in-app-sms/
Essentially:
MFMessageComposeViewController *controller = [[[MFMessageComposeViewController alloc] init] autorelease];
if([MFMessageComposeViewController canSendText])
{
controller.body = @"SMS message here";
controller.recipients = [NSArray arrayWithObjects:@"1(234)567-8910", nil];
controller.messageComposeDelegate = self;
[self presentModalViewController:controller animated:YES];
}
And a link to the docs.
https://developer.apple.com/documentation/messageui/mfmessagecomposeviewcontroller
One of the systems of inter-process communication in MacOS is XPC. This system layer has been developed for inter-process communication based on the transfer of plist structures using libSystem and launchd. In fact, it is an interface that allows managing processes via the exchange of such structures as dictionaries. Due to heredity, iOS 5 possesses this mechanism as well.
You might already understand what I mean by this introduction. Yep, there are system services in iOS that include tools for XPC communication. And I want to exemplify the work with a daemon for SMS sending. However, it should be mentioned that this ability is fixed in iOS 6, but is relevant for iOS 5.0—5.1.1. Jailbreak, Private Framework, and other illegal tools are not required for its exploitation. Only the set of header files from the directory /usr/include/xpc/* are needed.
One of the elements for SMS sending in iOS is the system service com.apple.chatkit, the tasks of which include generation, management, and sending of short text messages. For the ease of control, it has the publicly available communication port com.apple.chatkit.clientcomposeserver.xpc. Using the XPC subsystem, you can generate and send messages without user's approval. 
Well, let's try to create a connection.
xpc_connection_t myConnection;
dispatch_queue_t queue = dispatch_queue_create("com.apple.chatkit.clientcomposeserver.xpc", DISPATCH_QUEUE_CONCURRENT);
myConnection = xpc_connection_create_mach_service("com.apple.chatkit.clientcomposeserver.xpc", queue, XPC_CONNECTION_MACH_SERVICE_PRIVILEGED);
Now we have the XPC connection myConnection set to the service of SMS sending. However, XPC configuration provides for creation of suspended connections —we need to take one more step for the activation.
xpc_connection_set_event_handler(myConnection, ^(xpc_object_t event){
xpc_type_t xtype = xpc_get_type(event);
if(XPC_TYPE_ERROR == xtype)
{
NSLog(@"XPIf you want, you can use the private framework CoreTelephony which called CTMessageCenter class. There are a few methods to send sms.