Apple has released iOS 4.1 beta for developers and may roll out public version of iOS 4.1 soon. So, if you want to jailbreak and unlock iPhone 4, you should save iPhone 4 SHSH blobs for iOS 4 on Cydia Server. Here is how to do it:

How to Save iPhone 4 SHSH Blobs for iOS 4 on Cydia

Step 1: Download TinyUmbrella aka FirmwareUmbrella for Windows, Mac OSX or Linux / Ubuntu

Step 2: Run TinyUmbrella

Step 3: Connect iPhone with Computer and Sync with iTunes

Step 4: In TinyUmbrella click on “Save My SHSH” button on top left.

Step 5: Let the process complete, TinyUmbrella will show messages:

SHSH SUCCESSFULLY saved! [Click Here to Open]

You have saved your SHSH locally and the request was sent to CYDIA. This means that CYDIA DOES have your SHSH. Do NOT bug semaphore about the Cydia home page showing this version.

When this message shows up, you should feel safe for iOS 4 jailbreak and unlock since you have successfully saved iPhone iOS 4 SHSH blobs on Cydia Server. So you can always downgrade to iOS 4.