iphonejtag published a 10 Step procedure that appears today as the best way to SIM-unlock an iPhone. But it is far to be the easiest one available, as it implies disassembling the iPhone, as well as soldering micro-wires on the motherboard:
This is probably the most difficult part, as the track on the PCB is far to be large, and its thickness is in the micrometer range. There are high risks of crating short-cuts between to adjacent tracks on the PCB.
But your need to perform this step as it is so far required to be able to modify the firmware.
iPhone fans not living in USA can purchase such SIM-unlocked iPhone from eBay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230164884672
