If you're on a call on line 1 and a second call comes in and your phone doesn't ring nor does your headset beep to notify you; it's more than likely a setting in MXIE. Do the following and test.
- Launch MXIE
- Click on File | Preferences
- In the menu on the left, click 'Device Access Policy"
- On the right, under 'For multiple incoming calls', select "Manage using the phone"
- Click [Apply] and then [OK]
Test to see if that resolves the issue.