Unable in reading SMS from 3g USB dongle

问题

I'm building a windows service to read SMS from 3G dongle storage set as SIM card using AT commands. It's working good but some times it fails and response shows +CPMS: 0,0,0,0,0,0.

Code

        gsmPort.WriteLine("AT+CMGF=1"); //Set mode to Text(1) or PDU(0)
        gsmPort.WriteLine("AT+CPMS=\"SM\""); //Set storage to SIM(SM), MODEM(ME), BOTH(MT)
        gsmPort.WriteLine("AT+CMGL=\"ALL\""); //What catagory to read ALL, REC READ, or REC UNREAD

        response = gsmPort.ReadExisting();

When i move dongle into another port it starts working. I've tride it on multiple systems with different dongle but the result is always same. I've also changed my SIM card but no effect. Can any one have any idea why after some time SIM storage shows 0/0.

来源：https://stackoverflow.com/questions/42506759/unable-in-reading-sms-from-3g-usb-dongle