iPhone 3GS bricked ;(

Your description says your IMEI is xx145xxxxxxxxxx (which is good). I assume you read the iPhoneHacks article. It says there that if your IMEI is xx135xxxxxxxxxx, you should not install the iPad baseband. But in this case, the iPad baseband's side effect may be remediated.

The latest redsn0w application (version 0.9.15 beta 3) gives you an option to downgrade from iPad baseband under the Jailbreak section. Assuming you currently have iPad baseband installed (06.15.00), you should tick the box "Downgrade from iPad baseband" then proceed with the normal jailbreak operation (Uncheck everything but Downgrade). If it gives an error, go to Extras then select "Browse" and point the file to a stock IPSW. Redo the steps above and this will fix your baseband issue.

If the first solution didn't work, try booting the phone in DFU (or pwned DFU if it failed). iTunes will then tell you that it detected an iPhone in recovery mode. Perform a normal Restore and this may fix the issue.

To check if the downgrade was successful, your baseband should show 05.13.04 (or any but not 06.15.00).

Let me know if it works :)