From my observation and opinions from a friend of mine, switching to and from iPhone can be a pain. It doesn't detect the contacts in the SIM card, so you'll have to key them in one-by-one. My housemate spent few nights to transfer all his contacts to his iPhone. I can't imagine what will happen when he wants to switch to another phone later.

Well, I am not an owner of iPhone, so better hear from iPhone owners personally. I may be having the wrong impression on the matter. =)