What is difference between iphone and iphone 3g

Yes, provided the iPhone 3G is not locked with any other different network. If it is then, you need to unlock the iPhone.To unlock an iPhone the remote unlock service would be a better option because, you need not give your mobile to someone else nor do you have any chance to enter the wrong unlock codes. To get such an unlocking service for your iPhone 3G approach Wickedunlock.com and by submitting the country and network to which the mobile is locked to you will be able to remove the restriction from the respective network. This will be a permanent unlocking solution. Once unlocked you can swap networks.The iPhone 3G supports Mini sim...and hence insert the respective sim size.

the main difference between the iphone 3g and iphone 3gs is the speed. but here are the specifications for both phones
weight: the 3gs is slightly heavier at 135g memory: iphone 3g only has two options an 8gb or a 16gb whereas for the iphone 3gs it has 8gb/16gb/32gb camera: the iphone 3g has 2mp camera that can only take pictures while the ihpne 3gs has a 3.15mp camera that can also capture videos cpu/processor: iphone 3g has ARM 11 412 MHz, PowerVR MBX-Lite graphics while the iphone 3gs has 600 MHz ARM Cortex A8 processor, PowerVR SGX535 GPU. So the 3gs is faster and it means less or no lag on apps
the 3gs has a digital compass
and the 3gs has a longer battery time than the 3g.
to summaarize, the iphone 3gs is faster, has longer battery life, and has a bigger memory (as it comes with a 32gb version).

I think it may not Unlocked 100% what Method You used for Unlocking,You can get the Unlock code at reliable cost at here
http://www.theunlockarena.com/apple-iphone-3g/rs13wp9/ and Unlock it,use any GSM Sim card,.

i dont think the iphone will pair with the tom tom gps, because they use a different satellite & interface....iphone is running on Google whereas tom tom has its own satellite.

You will need to update the internet settings for your network.

I am going to say, no. Not only would most likely ruin the phone to remove the back, but the original iPhone and the iPhone 3G are actually a slightly different shape, and I am sure that the internal workings would make the backings entirely incompatible. If you aren't short on money and you REALLY want a better looking backing for your iPhone, check out http://www.colorwarepc.com/default.aspx I don't know if they still will do original iPhones, but they might. Plus, that way, you don't even have to be limited to black and white. Hope that helps.

No 2g and 3g screens are compleatly diffrent

The iPhone 3G has all the features of the first one,
plus faster 3G data downloads,
GPS, and a better battery life.
Externally, the phone's casing is slightly changed, with a thinner edge and thicker middle, but a flush headphone jack and solid-colored back make up the only other major differences visually. Everything else from the screen to the number of buttons and switches on the outside are the same.