Posted by: ranasaggy May 25, 2010
How to unlock Iphone 3gs with baseband 5.12.01 and the OS 3.1.3 ?
Login in to Rate this Post:     0       ?        
For sure Dude !!! You need to jailbreak and unlock to be able to use Iphone in Nepal.
The main thing you asked about downgrading is:
It is POSSIBLE if you had upgraded your Iphone via Cydia using its guidance.
But IMPOSSIBLE if you had done it via something else.

Hope this helps you out.
Read Full Discussion Thread for this article