I have an iPhone 4 that I got from my uncle (it's a little used), but I don't have the original SIM that came with that iPhone, and I want to unlock it, can I ask the old carrier to unlock it with only the IMEI and others information that do not depend on the SIM card? Will it be able to receive a carrier settings update on iTunes?
Yes. Carrier settings are sent when you connect to their respective cellular service. So if you purchased an unlocked iPhone 4 from Apple, and inserted a SIM from AT&T, you would be pushed the latest carrier update. If the next day, you removed the AT&T SIM and inserted one from Bell Mobility, then you would be pushed a carrier update for that respective carrier.
The updates are based on your iOS version number and the wireless network you are connected to (of course you need the respective SIM as well). You won't receive updates should you remove the SIM (or fail to insert one), but then it becomes a moot point because you need the card to connect to a network, making a carrier update rather pointless to begin with.
When the original carrier unlocks the device, it will be able to handle any wireless network. And the new carrier you sign with, will issue you a SIM.
Been having the same problem for 4 months. I backed up and restored and it still didn't worked. I was pretty bummed out..and I really didn't want to go to a repair shop for phones cause they cost a tonnnn! So I just randomly thought that maybe something sticky got inside the button and used a pair of eyebrow tweezers (the pointy ones like this one: http://ecx.images-amazon.com/images/I/31xBWTSHbiL.jpg) and I basically just stuck it around the button maybe 3 or 4 times really well and TADA! I DON'T HAVE THE ISSUE ANYMORE!!! I'm so happy I saved money by not getting it repaired :'D