Aastra 6757i CT User Manual page 296

Lock the Phone
2. In the "Lock the Phone?" field, click Lock.
The phone locks dynamically and displays the following message:
"Phone is locked".
Unlock the Phone
3. Click on Operation->Phone Lock.
4. In the "Unlock the Phone?" field, click Unlock.
The phone unlocks dynamically and displays the following message:
"Phone is unlocked".
Model 6757i CT IP Phone User Guide 289