hi
i have problem with my iPhone.
i updated my phone to 3.1 and unfortunately the basband and bootloader both ware updated too, & installed ultrasn0w
to unlock it, but this did'nt work so i downgraded to 3.0 and it's still not work and giving the no service error.
can somebody tell how to downgrade it to 3.0?

You're stuck, there is no way to downgrade your baseband on your iPhone. There is no unlock for this new baseband, it is likely there will not be an unlock. However there are people still looking into developing an unlock, it is a lot harder than it was previously because apple has cleaned the baseband up a lot more.

Just to be clear you only upgraded the baseband. The bootloader was always 5.9

Only those lucky people who purchased 3G iPhones with 5.8 bootloader have the capability to downgrade baseband.

tanks,
i will wait for the new hack,