Can I update restore iPhone 3GS with IPad baseband to 5.1?

[Jlhernan]

I don't need to jailbreak anymore since my phone is unlocked now and want to go back to stock firmware.
I need to know:
1. if I update/Restore from iTunes, would my phone be ok? Or would I still need to restore from custom firmware?
2. If i can restore, would that update my baseband to the current version? Or is It even possible to remove iPad baseband?

 

[iDonev]

Since you're running iPad baseband "ordinary" updates are impossible. You'll always get an error (I believe it's the "Your device is not eligible"). So you'll have to run with custom firmwares.

In case you want to run stock iOS, sn0wbreeze offers Baseband Preservation Mode when creating custom IPSWs, meaning you'll preserve your basebaind, but not install Cydia.