new iphone need assistance please

[renderpimp]

ok first off hi as im new to the forums.
right my mate bought an iphone in january and had it hacked by them to work on orange, then he bought a new orange iphone and gave me his old one (which he didnt use for mnths). so the problem is i am on o2. I need to know how and if i can jail break it so i can use it with my o2 sim card. below are some details regardning versions on the phone.

version :2.1 (5f136)
carrier 2.6
model mb496b
modem fimware 02.11.07
i have a feeling it has been jail break before as i have cydia in the icons on the front screen. the hack the company used for my mate was a hardware chip adapter on his sim. this doesnt work on mine.

any idea what i can do to resolve this please.

 

[SuperTrouper]

Have you tried putting your O2 SIM in without the hardware adapter?

 

[renderpimp]

yes the bars on the left corner do nothing

 

[jamesus]

Have you tried downloading yellowsn0w from Cydia?