I recently exchanged my iPhone for a Samsung Galaxy smart phone.
I was delighted to find that the iPhone still works with data transmission on Wi-Fi without a SIM card. All the apps still work and I can send and receive emails. The iPhone is certainly not a throw away device and still extremely useful as a mini-computer.
The only feature that has been lost with the removal of the SIM card is the ability to send and receive telephone calls and text messages and connect using 3G. Needless to say it requires a Wi-Fi to function.
I you are not sure how to connect your iPhone to Wi-Fi then watch the video below.