If your MiiTel Phone screen looks like the image below, the following may be the cause of the problem.
Other users are using your account at the same time
With one MiiTel account, you can log in and activate multiple MiiTel phones. For this case, when you make a call on one MiiTel Phone, the remaining MiiTel Phones will display "Calling" as shown above. When the user ends the call, the screen will return to the pending screen.
Your other MiiTel Phone still shows the conversation memo screen
If Auto ACW feature is on, the phone will be considered to be in use, even when the user is having the call memo screen displayed. If you are logged in to multiple MiiTel Phones with the same account, you will see the "Calling" screen shown as above if one of the MiiTel Phones is displaying the call memo screen.
You can use the MiiTel Phone by finishing the entry of the call memo and setting the phone to the pending screen.