Can you sync facebook contacts with the iphone 3g?

There's no sync option under facebook friends in the facebook app.

To sync your Facebook Friends with your iPhone Contacts:

Be sure to download the latest version of the iPhone App from the Apps Store, without it you will not be able to sync your Facebook Contacts.
After your app is updated, Open Facebook on your iPhone.

From the Facebook Landing page click the Friends button.

Next, Click the Sync button in the top right corner

On the next screen slide to Yes the Syncing option, and if you'd like to pull in the profile pictures from Facebook, slide to Yes the Replace Photos option

Accept the agreement screen that displays to allow Facebook to start syncing up your Facebook Friends with your iPhone Contacts.

Your Facebook Friends information should start downloading from the Facebook server and syncing up with Address Book on your iPhone to keep the contact information of your friends up to date.

Now that you've pulled down the latest contact information from Facebook to your iPhone you can open up Address Book and see the changes to your contacts. Many of your Friends Contact information will include their latest profile picture on Facebook as well as a "website" link to their Facebook Profile.