Syncing

Sync your old 3G, then when setting up the 4 restore to get an exact duplicate of what you had on 3G (assuming that is what you want). Setting up as new won't restore your apps, data, etc, it will act like a second separate phone.

set it up however you want.

When first connecting the iPhone to iTunes, you will activate the iPhone first. After the iPhone is activated, you will be prompted to transfer the backup for your 3G or set up as new. Either way, this must be followed by a sync to transfer your selected content under the various tabs for your iPhone sync preferences from your computer to the iPhone.

Once you connect your new phone to iTunes it will take you through the process - just read each screen carefully, and choose the options you want.

If you want to duplicate everything you have on your current phone, apps, data, etc - it won't be a problem. It even copies over all the ringtones, and any specific contact ringtones. Copies your voicemails, etc.

The only data you will have to re-enter are the passwords on your email account(s) - I suppose this is for security purposes.

Piece of cake - enjoy!