iPhone Cannot unlock iphone 3g running ios 421 using redsnow or ziphone

Hi chaps.
I have been trying to unlock my iphone 3g using redsnow and or ziphone.
I have followed the instructions given as well as many videos on youtube and I always get the error mesage that my iphone has not been recognised.
Is there a simplier way to unlock it so I can use a different provider as it is lock to O2.
the specs are:
Iphone 3g 8gb version 4.2.1 (8C148)
carrier O2 9.1
Firmware 05.15.04
I have tried to put a different sim from Orange to do a network search then reboot as it was suggested on another forum but in vain. I am always locked on O2
Thanks in advance for your suggestions.
Marty

hi mate ziphone is the old way of unlocking on fw if you are unlocking with a soft ware unlock you need jailbreak using redsn0w then ultrasn0w to unlock your device

biffo1 said:

hi mate ziphone is the old way of unlocking on fw if you are unlocking with a soft ware unlock you need jailbreak using redsn0w then ultrasn0w to unlock your device

Click to expand...

Hi biffo.
Thank you for your reply.
As I said when I use redsn0w_win_0.9.6rc16 I follow the instructions to enter in dfu mode and at the end of the process I always get the following message:No device detected, you probably misunderstood the instructions...
I am using the right software provided (iphone restore 1,2_4.2.1_8C148_restore) and when running redsnow I right click the programm to run it as addministrator as well.
Nevertheless I am getting nowhere. I get a black screen and nothing happens. It looks like during the dfu process it tries to put me straight into dfu before the whole process has been completed.

if your on windows 7 have you right clicked the redsn0w exe file gone to properties then compatability tab and choose run in windows xp service pack 3 tick then apply try that

Thanks for your reply Biffo.
I have tried your suggestion with no result unfortunately.
When I press and hold the power button the apple logo starts appearing.
Midway through the second phase of the process when I hold both power and home buttons the apple logo disappear and all I am left with is a black screen (like it switched off) and then by the end of the 3 stage I always get the error message.
I have been trying for weeks now and I am running out of ideas as to why it is not happening.

hi mate sorry i just read your 1st post again redsn0w wont unlock your iphone just jailbreak it , and restore , and other bits, ultrasn0w is used to unlock your device which you have to jailbreak your device to do so , can you explain if you want to jailbreak using either redsn0w or Greenpois0n and unlock

yes i am trying to jailbreak and then unlock so I can use a different mobile phone operator.

you cant unlock the 05.15.04 baseband with ultrasn0w

you will need to update the baseband to 06.15.00 then downgrade it to 05.13.04.
there was a thread the other day that shows you how to upgrade/downgrade the baseband: https://www.digitalworldz.co.uk/index.php?threads/292995/
you dont have to downgrade the baseband from 06.15.00 but i recommend you do as the ipad baseband kills the GPS.

then you need to jailbreak it, i would go with greenpois0n for the 4.2.1 jailbreak: https://www.digitalworldz.co.uk/index.php?threads/257073/

then after jailbreaking install ultrasn0w from cydia: [Tutorial] How to Unlock your iPhone 3G/3Gs/4 with Ultrasn0w
now your phone is unlocked.