Let me take this opportunity to warn you again. If you’re using ultrasn0w to unlock your iPhone 3GS or 3G, remember not to update to iPhone OS 3.1 directly via iTunes when it’s released. You may end up losing the ultrasn0w unlock. That is, you cannot make call or receive call. So, even iTunes prompt you for the iPhone update, remember to say “No” and wait for iPhone Dev team to give you the green light.

According to iPhone Dev Team:

If you update to Apple’s new software using the normal iTunes process, you will lose your ultrasn0w unlock. In fact you may lose it permanently, because for most people the baseband firmware cannot be reverted to a previous version (unlike the main application CPU firmware).

But don’t worry…our PwnageTool program let’s you update your main firmware without touching your baseband firmware, so you can still have the best of both worlds. But you must be diligent about saying “no” to your iTunes request this week to update your firmware.