i've upgraded to a 4s leaving my old 3gs sat at home but my wife wants the phone. she's on orange and the phone is locked to o2, am i right in thinking jailbreaking it will unlock it's network too?

i always fancied jailbreaking it when i was using it but was too scared incase i shafted it and was left with no phone but now it's not essential anymore i'm tempted!

any advise on jailbreaking the phone? i'm no I.T. geek but can find my way around things with a few pointers.