Q: im using iphone 4s, why after update the ios 6.1.3 it shows that "the iphone cannot be restore at this time because the iphone software update server could not be contacted or  is temporarily unavailable? how couldthis happen and what should i do?

Take a look at this Apple doc -> iOS: Resolving update and restore alert messages

1. Update to the latest version of iTunes

To see if you have the latest version of iTunes, open iTunes and check for updates.

• Windows: Choose Help > Check for Updates
• Mac: Choose iTunes > Check for Updates

Install any available iTunes updates. If you are using Mac OS X 10.5.8 (Leopard), you may need to download and install iTunes 10.6.3. If you do not have an active connection to the Internet, or if your Internet security settings are configured to prevent iTunes from communicating with Apple, iTunes will alert you that the update server could not be contacted. Resolve your Internet issues and attempt to update again.

• If you are using Windows, see iTunes for Windows XP: iTunes cannot contact the iPod, iPad, or iPhone software update server and iTunes for Windows: Network Connectivity Tests.
• If you are using Mac OS X, see    Mac OS X: Connect to the Internet and troubleshoot your Internet connection.