Archived:Using CommConnection with COM ports from MIDlets on S60 3rd Edition (Known Issue)
When the phone has been connected to some other device (usually PC) with a cable, you can open a CommConnection in a MIDlet running on that phone, and use that connection to communicate to an application running on the other device.
However, if you try to open a CommConnection using COM0 or COM1 (or any COM port), and also USB0 with certain S60 3rd Edition, FP1 devices, the MIDlet will either exit without warnings, or throw a 'SymbianOSError= -21 General' error. On S60 3rd Edition, FP2 the system returns the error code "Feature not supported".
It is also possible to query the system for available ports using System.getProperty("microedition.commports"). Even if this method call returns some COM ports on S60 devices, those should not be used for opening a CommConnection.
Open the CommConnection using the available USB ports. On certain S60 3rd Edition, FP1 devices, use USB1 if USB0 throws an error.