In certain situations, iPhone 4S may have difficulty recognizing a micro-SIM card, resulting in the following behaviors:

"Invalid SIM" or "No SIM Card installed" alert appears intermittently.
Status bar displays "No Service" or "Searching" in a location with good network coverage.

Read recommendations and guidelines for cleaning your Apple computer, iPad, iPhone, iPod, display, or peripheral device. 

You may be unable to set the time zone on your iPhone or iPod touch.

When moving an event from one calendar to another as follows:

Launching the Calendar app on an iOS device that has a MobileMe account set up with at least two calendars (such as Home and Work).
Selecting an event in a Home calendar.
Moving the event from Home calendar to Work calendar.

You may see:

Calendar events duplicated on me.com/calendar or in other applications syncing your calendar data (such as iCal or Outlook).
Calendars out of sync on me.com/calendar or in other applications syncing your calendar data (such as iCal or Outlook).

Learn what you can do if, after setting up Home Sharing, you cannot access your shared iTunes library over your home network from another computer, Apple TV, or iOS device.
Note: For general information on Home Sharing, see Understanding Home Sharing.

Home Sharing in iTunes is designed to let you easily share your iTunes media libraries between up to five computers in your household. You can also use Home Sharing to play your iTunes content on your iOS devices and Apple TV (2nd generation) if they are connected to your home Wi-Fi network.

You may want to restore your iPhone, iPad, or iPod touch and set it up as new to troubleshoot an issue. Take steps to preserve your data before restoring as new by following this article.

You can use a passcode on your iPhone, iPad, or iPod touch to protect your information and data. Each time you turn on or wake up the device, it will prompt for the passcode before you can access applications or information on the device.
This article provides resources and tips for using passcodes. For full details on passcode lock and settings, refer to the User Guide for your product.

When you sync an iPhone, iPad, or iPod touch with a Windows computer, one or more of the following alerts may appear:

"The [device] could not be synced. A folder was specified instead of a file."
"The contents of the iPhone could not be read. You must restore the iPhone"
The "Set up your iPhone" prompts may reappear after each time you reconnect the device, even after fully setting up the device’s sync options.

The steps below may resolve the issue.