自己写了个调起打电话的类，只需要修改一点点就可以直接使用：

//
//  HYBPhoneCallHelper.h
//  XiaoYaoUser
//
//  Created by 黄仪标 on 14/12/16.
//  Copyright (c) 2014年 xiaoyaor. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface HYBPhoneCallHelper : NSObject

// 调用默认客服电话
+ (void)call;
+ (void)callWithPhone:(NSString *)phone;
+ (void)callInController:(UIViewController *)controller;
+ (void)callInController:(UIViewController *)controller WithPhone:(NSString *)phone;

@end

#import "HYBPhoneCallHelper.h"
#import "HYBCommonAlertView.h"
#import "HYBAppCommonInfoTool.h"

@implementation HYBPhoneCallHelper

// 调用默认客服电话
+ (void)call {
  [self callWithPhone:[HYBAppCommonInfoTool servicePhone]];
}

+ (void)callWithPhone:(NSString *)phone {
  NSString *teleString = [NSString stringWithFormat:@"tel://%@", phone];
  NSURL *teleUrl = [NSURL URLWithString:teleString];
  if ([[UIApplication sharedApplication] canOpenURL:teleUrl]) {
    [[UIApplication sharedApplication] openURL:teleUrl];
  }
}

+ (void)callInController:(UIViewController *)controller {
  [self callInController:controller WithPhone:[HYBAppCommonInfoTool servicePhone]];
}

+ (void)callInController:(UIViewController *)controller WithPhone:(NSString *)phone {
  HYBCommonAlertView *alert = [[HYBCommonAlertView alloc] initWithFrame:CGRectMake(0, kScreenHeight, kScreenWidth, 140) title:@"咨询投诉、应聘美容师可拨打客服电话。" leftBlock:^{
    [self call];
  } rightBlock:^{
    DDLogVerbose(@"cancel to make a phone call");
  }];
  [alert showInController:controller];
}