How to distinguish an iPhone 3GS from a 3G?

[jacoscar]

Hi everibody, I just bought from a guy a broken iPhone 3GS 8GB (doesn't turn on)
When I arrived at home I checked the imei written on the sim tray on Check IMEI - IMEI.info and it said it's a 3G
The guy replied it could be the tray from another phone, but... how can I be sure? Since I have to order spare parts I wanna be sure I'm getting the right spares...
I opened a 32gb 3gs and the display connector seems a bit bigger than the assumed 3gs 8gb

 

[willerz2]

The model number on the back of the iPhone will determine which iPhone it is. Unless the plating was changed. 9 out of 10 sellers that are selling a 3G will almost ALWAYS throw out the point that "The SIM tray is from a 3GS" when the device is clearly a 3G. Reason is that the 3G doesn't sell but the 3GS does. Consult this list

Identifying iPhone models

 

[jacoscar]

The model number on the back of the iPhone will determine which iPhone it is. Unless the plating was changed. 9 out of 10 sellers that are selling a 3G will almost ALWAYS throw out the point that "The SIM tray is from a 3GS" when the device is clearly a 3G. Reason is that the 3G doesn't sell but the 3GS does. Consult this list

Identifying iPhone models

I've checked the serial number on the logic board and it's actually a 3GS 8gb
I also noticed the different shape of the sim reader and I'm sure it's a 3GS

I still don't understand however why the LCD does not fit (the connector was unplugged)

 

[GazNicki]

Also if you are opening the phone up and remove the screen, the dock on the bottom will have connector #7 attached to it if it is a 3GS. The 3G doesn't have connector 7.

 

[ricearoni420]

Try this page http://support.apple.com/kb/HT3939

 

[BLAKESCARTH1992]

Hold the home button see if you get commands if not its a 3G

Sent from my iPhone 4S 64gb

 

[Beast from the East]

U can try camera, if u can focus with finger, its 3gs

 

[WSE7670]

Check the version. 3G can only be upgrade until 4.2.1. Connect to Itunes to find out if the 3G can be upgrade to the latest ios or not. If can, means your device is 3GS not 3G.