I'm on the iPhone firmware 2.1 (with old baseband).
Does anyone know, can I update only the baseband to 02.28.0
and then use yellowsn0w to unlock it?

Thanks

It's the only way to unlock it.

Update through itunes to 2.2, then quickpwn, then add apt9.yellowsn0w.com to sources. Refresh, install yellowsn0w, reboot. Tada, unlocked iphone 3g

Edit: just noticed you are asking to keep 2.1 soft. My bad. Why would you want to keep 2.1?

I'm lazy enough to back up the data and then re-install all my apps on the new firmware

I found some tutorial that use BBUpdaterExtreme to update baseband only in a few minute without nuking the data.

So, I just curiuos is the firmware 2.1 can run on the baseband 02.28.0

2.1fw can run baseband 2.28.0. But as far as i know, to do you that you have to use mac, make a custom firmwire upgrade, then jailbreak and install yellowsn0w. trust me, too much work. back up and installing 2.2 is much more less work.

Code:

Manually Upgrade Baseband.

Code:

Or this guide to clean restore.

cool,
I'll try it, and will post the result here, thanks.