Could not find any recognizable digits when check sms in gsmcomm

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C#

C#4.0

SMS

GSM

I used gsmcomm library to develop little sms program, but when i click in btnCheckSMS i got the string error like this "Could not find any recognizable digits " . this button used for reading incoming sms in the gsm sim card. This is my code :

private void btnCheckSMS_Click(object sender, EventArgs e)
    {
        var messages = comm.ReadMessages(PhoneMessageStatus.All, PhoneStorageType.Sim);
        foreach (var message in messages)
        {
            var data = (SmsDeliverPdu)message.Data;
            var phoneNumber = data.OriginatingAddress; // when debug got the problem over here, Could not find any recognizable digits 
            var msg = data.UserDataText;
            var tanggal = string.Format("{0:yyyy/MM/dd}", data.SCTimestamp.ToDateTime());
            var jam = string.Format("{0:HH:mm:ss}", data.SCTimestamp.ToDateTime());


            lstDaftarSMS.Items.Add(string.Format("{0}, {1}, {2}, {3}", tanggal, jam, phoneNumber, msg));
        }
    }

when debug got the problem over here, Could not find any recognizable digits :

var phoneNumber = data.OriginatingAddress;

anyone can help me how to solve this?