如何在Objective C中拨打电话？

NSString *phoneNumber = @"1234567890";
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"telprompt:%@", phoneNumber]];
if ([[UIApplication sharedApplication] canOpenURL:url]) {
    [[UIApplication sharedApplication] openURL:url];
} else {
    NSLog(@"无法拨打电话");
}