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First thing we want to do is to check to see that you don't just have a filter on the contacts-
Main Menu > Contacts > Menu Button > Filter > and make sure everything is checked
-You may also want to eject your SIM card and reinsert it if you are using SIM contacts instead of Google.
-If you are using Google contacts, log onto your gmail account and verify that all your contacts are listed there. If they are, go into your phone and go into settings > accounts and sync > google > click on the email address listed at the top and make sure that contacts are being synced.
If the sync is checked but they are showing that they are not syncing, go into the menu and try "sync now". If this fails and you are connected to the internet, remove the account and add it back and see if that resolves the issue.
If these tips do not resolve the issue please feel free to re-post the issue again, or register an account so you can interact with the entire community.