Nope. I've unlocked my 3G and 3GS and they had SIM in it. I then put in my T-Mobile SIM from my Blackberry to test, rebooted phone and it worked fine.I am planning on jailbreaking/unlocking my old 3g and selling it on ebay. One thing that is confusing me is the SIM card. Do I need to jailbreak/unlock without a SIM card installed to ensure it will work with any carrier?
Glad it worked out.Applejuiced, Thanks for the great info. I did the UltraSn0w from Cydia, per your instructions. Everything works perfectly!!!! This whole process was all very easy actually. I tried several different SIM's, from different parts of the world that I travel too, and they all worked.
Now, the next question is, do I really need an iPhone 4? Probably will get one and keep the 3G for my international travels.