Notifications let you know if you missed a call or IM, or anything else when you’re not actively using the Lync app. Notifications also let you know if there is an issue with the app, or if you need to take any action. You can set notifications so they’re displayed as a banner or alert message, and with or without a badge application icon. You can also have a sound played when you receive a notification.
You choose how to display notifications from your iPhone Settings.
From the Settings app, tap Notification Center, and then select Lync. Then select how you want notifications to be displayed.