This question must have been asked before, but I can't find where. Redsn0w doesn't make activation optional: if you jailbreak, you also 'hacktivate' the phone (which means, I think, the lockdownd binary is patched to make the phone think it was 'factory-activated' and some certificates are added for YouTube etc.).

If you're with an 'official' carrier, you obviously don't need hacktivation; iTunes will activate the phone with the carrier. I would think this is preferable: perhaps the phone company gets to see in its records that you properly registered, the binary is the original one, etc. But I'm no expert on this.

Is there someone knowledgeable who can shine some light on this issue? Is 'official' activation preferable, and is there a way to only jailbreak?

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iPhone 3GS / 3.1.2 JB (PwnageTool) / 04.26.08 carrier-locked, Carrier Logo Fixer / Cydia / 1000 posts on Hackint0sh

Installing Cydia programs on a phone that has no internet connection: read this.

Editing binary .plist, .strings, .nib and .xib files:
* on your computer: Windows tool / conversion website.
* on your iPhone: convert those files in a terminal with plutil (installed with Erica Utilities) or edit them with iFile (Cydia links).

i never could hacktiavate 3g simlocked phone.
it is one if these urban legends i guess.
if you look at tons of youtube videos these always use official sim with itunes
i do not know why blog says differently that you should use non-official sim - maybe to confuse evil company ?

Redsn0w only hacktivates if the phone isn't activated already. If it is redsn0w just bypass's that step.

Hactivation is not a process for the SIM itself but for the iPhone. redsn0w just tricks the phone into thinking that the SIM in the iPhone is an official one.

If you want to be 100% safe, use PwnageTool for jailbreaking. You can specifically activate/deactivate the 'Hacktivation' of your iPhone.

I don't trust redsn0w either because I haven't been able to find a clear official statement of one of the DevTeam members saying that redsn0w detects an already activated iPhone and therefore skips 'Hacktivation'.

It's just too delicate when you own a factory unlocked phone and don't have full control over things you do with it.

And by the way, redsn0w doesn't trick the iPhone into thinking that the inserted SIM is an official one. 'Hacktivation' patches files on your phone to fake-activate it.
For unlocking factory locked iPhones you have to use ultrasn0w or purplesn0w.

Official activation is preferable because you wouldn't need such nasty hacks for Push Notifications for example.

It's simple to do that. Once the restore is finished then just open iTunes and activate then run redsn0w.

From the Dev-team Blog:

"Remember, ultrasn0w works with hacktivated phones too, but don’t outsmart redsn0w into thinking you don’t need hacktivation! If you don’t plan on using an official sim, don’t activate via iTunes with such a sim. Just keep your unofficial sim at all times and let redsn0w and ultrasn0w handle hacktivation

So they say that redsn0w can be made to "think" you don't need hacktivation. Which strongly suggests that redsn0w will do something differently depending on whether it thinks that -- presumably it won't hacktivate if it thinks you have carrier-activated. Not a completely explicit statement, but the suggestion is clear.

Summarizing your answers,

1. Yes, carrier-activation is preferable to hacktivation "because you wouldn't need such nasty hacks for Push Notifications for example."
2. Most likely, redsn0w hacktivates only if you haven't carrier-activated.
3. Therefore, as long as you activate in iTunes before applying the redsn0w jailbreak, you're OK.
4. Alternatively, you can use Pwnage tool (but the Dev team hasn't released a 3.x version of that, so you'd need to modify some things).
5. For those who are confused: all of this has nothing to do with sim-unlocking (except that a jailbreak is a prerequisite for an unlock).

Thanks everyone.

__________________
iPhone 3GS / 3.1.2 JB (PwnageTool) / 04.26.08 carrier-locked, Carrier Logo Fixer / Cydia / 1000 posts on Hackint0sh

Installing Cydia programs on a phone that has no internet connection: read this.

Editing binary .plist, .strings, .nib and .xib files:
* on your computer: Windows tool / conversion website.
* on your iPhone: convert those files in a terminal with plutil (installed with Erica Utilities) or edit them with iFile (Cydia links).

I can copy that. i do have a factory unlocked 2G (really rare), 3G and 3GS. My friend got a 3G, his wife a 3GS both with legit contract.
All are at firmware 3.0.1 now, then activated in iTunes. After that we used redsn0w to jailbreak. No problems here at all, no notifications from the man in the moon.
The only important thing is that you activete first, before jailbreaking. Has been working the same way with QuickPwn before, btw. Both tools put the fake activation record(s) only if no activation record is present.

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iPhone 3GS factory unlocked (3.1.2; Blackra1n, Cydia, OpenSSH, custom 3.0 ipcc file (no sig), tethering hack by Dev team, 32 GB)
iPhone 3G (3.0.1; Redsn0w 0.8, Cydia, OpenSSH) 16 GB

Exactly. That's it summarized.

Thanks volkspost, that sounds reasonable to me.
Nevertheless I haven't updated to 3.0.1 yet. It seems like there's another SMS hack out there according to MuscleNerd which didn't get fixed with 3.0.1.
This time the carriers have to fix it anyways.

Another interesting statement from geohot referring to pointing redsn0w to an 3.0 .ipsw for jailbreaking 3.0.1:

So it seems like you're running the 3.0 kernel on 3.0.1 as soon as you're jailbreaking with redsn0w. Do you in turn lose the SMS fix?

Sorry for off topic :-)

that is just a lie. Maybe it happen to work for certain unoffical sims but not for mine