The gevey sim is in now way a permanent unlock for your phone. If you have an older gevey then after every reboot (regardless of firmware) you would need to go through the 112 method. With the new gevey ultra you would need to make sure that you are jailbroken and have the furiousmod installed, and wait for it to do its own unlocking in the background after every reboot.
+1. In a general sense if you upgrade to a newer firmware version released, the process is likely needed to be done again. But the question to ask is whether the Gevey will support the new firmware version and baseband, which I find not likely as Apple will patch it with the next major FW release.
The iPhone 4, latest firmware is 4.3.5 GSM, 4.2.10 CDMA.