The Sony Ericsson Device 091010 USB Serial Port is a driver used for enabling communication between a Sony Ericsson mobile device (typically older models) and a Windows PC via USB. The "USB Serial Port" typically refers to a virtual COM port that allows software on your computer to communicate with your device for tasks such as syncing, transferring data, or using the device as a modem. This driver was commonly used with older Sony Ericsson phones, such as those from the Xperia or Walkman series.