Few websites have come up with services to unlock iPhone 4 permanently with IMEI Unlock and there were also some news that IMEI Unlock is fake.
The websites which offer remote IMEI unlock could not guarantee permanent unlock to users as promised.
Veeence,of iPhone dev team confirms that Apple has the fixed the hole of their system which allows user to make requests for unlocks.
Time is up! Apple closed the hole for these official unlock requests (probably fired the employee). Don’t get scammed
He further tweets that,
Apple might relock your IMEI. Make sure you back up your activation token w/ SAM to stay unlocked in future. Important!
http://t.co/nOraQTMHowever, there are no reports till now regarding Apple blacklisting IMEI and relocking the phone.
@veeence is there any precedent of Apple blacklisting IMEI and relocking the phone?
@hsardaryan no reports yet.
It is advisable to stay away from websites which are offering permanent unlocking of iPhone.
iNews 
Apple Fixes IMEI Unlock Solution Of iPhone 4 ?