If you rely on ultrasn0w unlock, this might come in handy. Just follow these simple instructions to find out the modem firmware / baseband version of your iPhone 3G / 3GS / 4. This way you can be sure if you phone can be unlocked with latest ultrasn0w or not.
Step 1
Launch Settings from your Springboard.
Step 2
Select General from the Settings Menu.
Step 3
Select About from the General Settings Menu.
Step 4
From the about screen you can find your firmware version under the Version label.
Scroll down and you can find your baseband version under the Modem Firmware label.
(source iClarified)
