I don't see any icon for making phone calls and messaging on my iphone, but i still can receive call and messages. What do i need to do?

Reading your description and viewing the attached photo, i'm not sure i understand your query...

Your Phone application is the green square in the bottom left, and your messaging app is the green square in the top left.

Also, have you ever altered the software on your phone?

Curious as there is no carrier tag in the top left (between signal bars & "3G" and Newsstand shouldnt have to "D"s.

If however the attached image isnt of your phone,

then i would swipe to the right of your home screen to access Spotllight Search - and then Searching for "messages" or "phone".

Settings>General>Reset>Reset Home Screen Layout.

Is the iPhone jailbroken?

Did you try the 4Rs troubleshootings?:

1. Restart

2. Reset

3. Restore from backup using iTunes

4. Restore as new without the backup

Try it.

3. Connect and select iPhone in iTunes, Summary tab, click Restore Backup button.

4. ...ditto... click Restore iPhone button

Connect with usb cable and open iTunes.

Use your dock cable and connect iPhone to your computer.

You computer should have Internet connection.

http://support.apple.com/kb/ht1766

http://manuals.info.apple.com/en/iphone_user_guide.pdf

Open iTunes on your computer. Then connect your phone. Select it. Then click restore. You do everything through iTunes on your computer. Going to apple.com/iTunes will not do anything for you.