I unlocked my iPhone 4 with jailbreakme.com, and it was the fastest unlocking ever. Less than 5 minutes.
After buying a smartphone plan at Movistar, Argentina and fighting the whole week to get it to work, I found out the “carrier update” was good to install, and did something I forgot to do with this phone before, that AT&T and Apple recommends for a similar issue: turning on/off the phone, waiting a few minutes, airplane mode, 3G and cellular data on/off each, resetting network settings…
That got rid of the “no data plan…” message, and the processing wheel started to spin, no internet connection though.
Argentinian customer service reps never saw an iPhone at that service center. The guy who sold me the plan seemed to register the unit with a “Blackberry” code, not iPhone, but they concluded it should work fine anyway, even clearer when they put the SIM in one of their phones (I don’t know what brand) and it got data and the expected SMS configuration messages 
After doing all I found in internet by Sept 02 2010 for a whole week, I was about to return the plan to Movistar (Argentina).
I put the SIM in an iPhone 3G, which Movistar sells down here in Argentina (I had to re-build the SIM with extra card material) to test whether my data plan or my iPhone4 were wrong as a last resource.
When I put the SIM back into my iPhone4 to call Movistar to tell them they can put the data plan in their… it suddenly started to work.
Either the SIM told the carrier “yes, here’s a known device” when put in the iPhone3G or the scotch tape I used to cover the CHIP edges (the trimmed down SIM’s chip is bigger and may get in contact with the tray’s frame) fixed the issue.
I hope that helps.
About the author:Sergio Zambrano
Print designer until it started to die, Web Designer by hobby and Coder by force. Living in Miami and getting less sun than russians in winter, but I like Wordpress develpment even more.
