Q: Can you use an iPhone 3G without a SIM card as an iPod touch? I want my wife to have Wi-Fi access to the web and calendar use but no phone. I will upgrade to a 3GS if she can use the 3G like an iPod touch.
A: This is technically possible under certain conditions. Normally, the iPhone must be “activated” by iTunes in order for it to be used at all, and this activation process requires that the iPhone serial number (IMEI) and SIM card ID be checked with Apple’s servers to confirm that they are valid. This is the same process that you would have gone through when you initially purchased your iPhone.
However, once this activation process has been completed, you can remove the SIM card and continue using the iPhone and even syncing with iTunes without having to re-activate it. The only time that re-activation will be required is when you perform a firmware update on the iPhone, or perform a full “Restore” operation on it to return it to factory settings.
So in short, this means that you can use the iPhone on a day-to-day basis without a SIM card in it, and all of the non-cellular functions should work just fine, including Internet access over Wi-Fi. However, should you ever need to upgrade or restore the iPhone, you will need to insert a valid SIM card in order to complete the activation process with iTunes. In the scenario you describe, however, this shouldn’t be a problem, as you should be able to just put your SIM card back into the iPhone and then carry on from there.
It’s also worth noting that jailbreaking the iPhone completely bypasses the iTunes activation requirements as well, although this is a slightly more advanced process and will probably not be worth the effort if your wife just wants to use the iPhone as a basic iPod touch style device.