iOS Error when sending email or sms

I'm trying to send sms and email from an iOS app, but I encounter some problems.

I took the code from a tutorial, for example the sms code :

func sendMessage() {
    let prefs = NSUserDefaults.standardUserDefaults()
    var message = MFMessageComposeViewController()

    // Contacts
    var phoneNumbers = [String]()
    var phoneNumberNb: Int = prefs.objectForKey("phonenumberssaved")!.count
    for(var i = 0; i < phoneNumberNb; i++) {
        phoneNumbers.append(prefs.objectForKey("phonenumberssaved")!.objectAtIndex(i) as! String)
    }

    println(phoneNumbers)

    message.recipients = phoneNumbers
    message.body = self.messageText
    message.messageComposeDelegate = self

    self.presentViewController(message, animated: false, completion: nil)
} 

and I printed my datas (they seems to be ok), but when I try to send it, the app crash with a

'fatal error: unexpectedly found nil while unwrapping an Optional value' and it show me a strange file with a line highlighted : '0x4b5164 <+64>: trap'...

via Chebli Mohamed