[spud5437]

I have bought my girlfriend an iphone from eBay, 8GB 3G but I see that’s its version 3.1.3 (7E18)
Can this be jailbroken? And if not can I downgrade a version?

[LVCIFER]

That depends. Are you familiar with the term "seek and ye shall find"? What about the whole concept of "search"? Maybe a little bit of investigation will lead you in the right direction. Maybe some elbow grease. Develop a little bit of carpel tunnel and do some typing on google.com.

Hell, this is the information superhighway! I'm sure you'll find something!

P.S.- My codolensces to your girlfriend. She's a trooper.