Thanks All For Your Answers...
I did it this way and it got me the required result
foreach (DataGridViewRow row in dgResult.Rows)
{
if (row.Cells[SelectColumnIndex].Value != null && Convert.ToBoolean(row.Cells[SelectColumnIndex].Value) == true)
{
objTempDevice.DeviceName = row.Cells["DeviceName"].Value.ToString();
objTempDevice.BroadworksDeviceId = row.Cells["BroadworksDeviceID"].Value.ToString();
objTempDevice.GroupId = row.Cells["BusinessVoIP"].Value.ToString();
objTempDevice.ServiceProviderId = row.Cells["ServiceProviderId"].Value.ToString();
lstDeviceDetails.Add(objTempDevice);
}
}