你可以使用这种方法:

[[UIApplication sharedApplication]openURL:[NSURL URLWithString:@"sms:MobileNumber"]]

iOS会自动从你的应用程序导航到消息应用程序的消息合成页面。由于URL的方案是从sms:开始的，这被标识为消息应用程序可以识别的类型，并启动它。

iOS 4中有一个类支持从应用程序中发送带有正文和收件人的消息。它的工作原理与发送邮件相同。你可以在这里找到文档:链接文本

- (void)sendSMS:(NSString *)bodyOfMessage recipientList:(NSArray *)recipients
{
    UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
    UIImage *ui =resultimg.image;
    pasteboard.image = ui;
    [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"sms:"]];
}

添加MessageUI。框架并使用下面的代码

#import <MessageUI/MessageUI.h> 

然后:

if ([MFMessageComposeViewController canSendText]) {
  MFMessageComposeViewController *messageComposer =
  [[MFMessageComposeViewController alloc] init];
  NSString *message = @"Your Message here";
  [messageComposer setBody:message];
  messageComposer.messageComposeDelegate = self;
  [self presentViewController:messageComposer animated:YES completion:nil];
}

以及委托方法-

- (void)messageComposeViewController:(MFMessageComposeViewController *)controller
             didFinishWithResult:(MessageComposeResult)result {
      [self dismissViewControllerAnimated:YES completion:nil];
 }

这是一个教程，它完全是你正在寻找的:MFMessageComposeViewController。

http://blog.mugunthkumar.com/coding/iphone-tutorial-how-to-send-in-app-sms/

从本质上讲:

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];
}

还有文档的链接。

https://developer.apple.com/documentation/messageui/mfmessagecomposeviewcontroller

下面是在iOS中发送短信的Swift版本代码。请注意，它只在实际设备中工作。在iOS 7+中测试的代码。你可以在这里阅读更多。

1)创建一个继承MFMessageComposeViewControllerDelegate和NSObject的新类:

import Foundation
import MessageUI

class MessageComposer: NSObject, MFMessageComposeViewControllerDelegate {
    // A wrapper function to indicate whether or not a text message can be sent from the user's device
    func canSendText() -> Bool {
        return MFMessageComposeViewController.canSendText()
    }

    // Configures and returns a MFMessageComposeViewController instance
    func configuredMessageComposeViewController(textMessageRecipients:[String] ,textBody body:String) -> MFMessageComposeViewController {
        let messageComposeVC = MFMessageComposeViewController()
        messageComposeVC.messageComposeDelegate = self  //  Make sure to set this property to self, so that the controller can be dismissed!
        messageComposeVC.recipients = textMessageRecipients
        messageComposeVC.body = body
        return messageComposeVC
    }

    // MFMessageComposeViewControllerDelegate callback - dismisses the view controller when the user is finished with it
    func messageComposeViewController(controller: MFMessageComposeViewController!, didFinishWithResult result: MessageComposeResult) {
        controller.dismissViewControllerAnimated(true, completion: nil)
        }
}

2)如何使用这个类:

func openMessageComposerHelper(sender:AnyObject ,withIndexPath indexPath: NSIndexPath) {
    var recipients = [String]()

    //modify your recipients here

    if (messageComposer.canSendText()) {
        println("can send text")
        // Obtain a configured MFMessageComposeViewController
        let body = Utility.createInvitationMessageText()

        let messageComposeVC = messageComposer.configuredMessageComposeViewController(recipients, textBody: body)

        // Present the configured MFMessageComposeViewController instance
        // Note that the dismissal of the VC will be handled by the messageComposer instance,
        // since it implements the appropriate delegate call-back
        presentViewController(messageComposeVC, animated: true, completion: nil)
    } else {
        // Let the user know if his/her device isn't able to send text messages
        self.displayAlerViewWithTitle("Cannot Send Text Message", andMessage: "Your device is not able to send text messages.")
    }
}