For anyone that got the 3G after having a 2G iPhone and wanted to erase all data on the 2G before selling it - would like you feedback. Here is what I think the process will look like:

1. Activate new 3GS
2. Sync it so it brings all my data/apps over
3. Erase all data from 2G using built in data wipe without needing to hook it up to iTunes
4. Sell old iPhone to buyer

I am pretty sure the new iPhone will come with a new SIM because I think the buyer needs a SIM in the 2G to activate or use it on his AT&T account.

As I was writing this, I found this AppleInsider | Secure data wipe built into iPhone Software v2.0 which I had not known about. Seems pretty straight forward now - I originally thought I'd need to connect to iTunes to erase old iPhone which I'd be afraid would cause problems.

[Mrjinglesusa]

There is no reason to leave your old SIM in your 2.0 iPhone when you sell it. The buyer should provide his/her own SIM card or they can get one from their carrier.

Unless they want to use it as an iPod / WiFi internet device then they will need a SIM card in the phone: Using an original iPhone without a wireless service plan

[Mrjinglesusa]

Originally Posted by Jmakkar 

Unless they want to use it as an iPod / WiFi internet device then they will need a SIM card in the phone: Using an original iPhone without a wireless service plan

I fully understand that. My point is that they can provide their own SIM card - either one they already have in a current phone or one they get from an AT&T store.

My point is that there is no reason for you to send them your SIM card.

[CorpITGuy]

Precisely. Your SIM is "burned" anyway. It cannot be re-activated on another number.