Is there a jailbreak for me?

[iGaz]

Jailbreak on the mac then sync it to the PC...

 

[osso12]

If you got your iphone from the shop with 4.2.1 on it like I did, you wont be able to have an untethered JB at all yet as you cant downgrade to 4.2b.

You can do a tethered Jailbreak with 4.2.1...Many of us have it already......
Just saying.... You do not have to downgrade to a "4.2.b" as there should be no distinction whether you bought it from a store or otherwise.

 

[iGaz]

You don't have to downgrade to 4.2b as that was a beta firmware only available to devs. You only need SHSH's for 4.2b which is possible to get if you had already pressed the 'make my life easier' button in cydia at the time apple were signing that firmware.

I have SHSH's for 4.2b having never been on that firmware. I even had 4.2.1 SHSH's stored when I was still on 4.1...