I have a Blackberry Pearl 8100 on an AT&T plan. Quite frankly, I feel a bit outdated with it and now planning on just buying a cellphone body from eBay like a Blackberry Curve or Storm, or even an iPhone. What does the term "unlocked" mean? And if it means what I think it means, can I use my AT&T sim card in an unlocked Blackberry Storm from Verizon? Or even an unlocked new iPhone 3GS? Will AT&T get wise and realize my phone is completely different, or will I still be able to use it as if I was still using my Pearl?