Help Unlock iphone 3G with 3.1.2, BUT NO WIFI

[bcncool]

How can I finish to unlock my IPHONE, if I don't have a WIFI connection.
My Iphone is 3G, it wasn't upgraded, so I have the old 3.1.2 I downloaded black ra1n but I can't proceed downloading cydia, since no wifi. How can I proceed. Thanks