Since iOS 4.01 is focused on signal bar display fix, Apple has not changed the baseband value in this update. The iOS 4.01 running iPhone devices will have same 05.13.04 baseband.
The good thing for unlockers is that the Ultrasn0w 0.93 will help you unlock these devices. Of course, there is no perfect jailbreak tool available for iOS 4 based iPhone 3GS and iPhone 4, which means you can only unlock iPhone 3G with Ultrasn0w tool.
The steps involved in unlocking the iPhone 3G are already given in previous tutorial, so you can check it out here. The Ultrasn0w 0.93 will also unlock the devices having 05.12.01 and 04.26.08 baseband.
If you haven’t jailbroken your iPhone 3G on iOS 4.01, follow this guide to jailbreak using Redsn0w tool. For more updates on iPhone, subscribe to Tech Exclusive.