Q: dear i purchased apple iphone 4 s from saudi arabia. i have checked all the setting available on apple website but my cellular data and 3g are still not working. i m really disappointed by apple product.

-> http://www.apple.com/sa/support/contact/

Cellular data and whether 3G works on your phone has nothing to do with the phone itself.  This is the responsibility of your phone company/carrier and is linked to the sim card that you have inserted into your phone.

You don't need to go to a service centre, but you do need to contact your phone company - cellular data and 3G is their responsibility and not Apple's.

Also, this is a public user forum, so you are not addressing Apple here.