What is the story with activation?

[irishdly]

Can anyone tell me how it works?

I have an Iphone 3g bought off e-bay that I accidentally upgraded to 3.1. Ive been able to jailbreak it (downgrading to 3.0, then uploading custom jailbroken firmware) but have been unable to regain network coverage (Using an O2 simcard). Ive even tried jailbreaking the 3.0 firmware which also works but still no coverage.
Looking at forum posts it seems that this is a problem if you do not activate your phone before jailbreaking.
Im not registered with the official carrier for my country (O2 Ireland). Im just wondering would I be able to activate the phone through Itunes using any O2 sim-card or does activation require the sim-card sold with the phone?

[blkcadi]

The jailbreak should have given you an option to activate it.
Have you tried using ultrasn0w to unlock the phone?

[irishdly]

Ive been on windows using itunes (8.2) to upload the the firmware. It always ends in a 1015 error and stuck in recovery loop from which I use irecovery to break out of. This always gets the Iphone activated, (either using the custom 3.1 firmware or redsnowing the 3.0) but I dont have network reception with an O2 simcard.
I cant unlock as I accidentely upgraded to 3.1 and my baseband was upgraded. Looking at the fourms it seems that this problem can be solved by legitimatly activating the iphone before jailbreaking. Im just wondering if this is an option for me seeing as I dont have the original sim-card that came with the phone.

[blkcadi]

Sorry, not that I am aware of. Can you use someone else SIM?

[irishdly]

I can get another sim yes, how would this help though?