3GS Activation after Jailbreak&Unlock

[balgat1167]

Here is my current specs :

IPhone 3GS (new bootrom)
Firmware : 4.2.1
Baseband : 5.12.0
originally AT&T locked, jailbreaked with snowbreeze, unlocked with ultrasnow and activated with SAM. Now working on another carrier.

Now, I am planning to upgrade to firmware 5.1.1 since this the most recent version with untethered jailbreak. I know that I can create custom ipsw with preserving the baseband with Redsnow , jailbreak and then unlock with ultrasnow. However if SAM is not working anymore, how to activate? At my previous upgrade to 4.2.1, when hacktivate via redsnow, I had issues with Youtube and it was then solved with SAM Activation.

Could some one please tell me the how to activate my phone step by step after jailbreak&unlock to 5.1.1 so that I don't have any issues/problems with the carrier/push/maps etc. What is the right method to activate? I have no AT&T sim card.

[balgat1167]

Read a lot of forums and it looks like I will lose Push notification, Facetime and iMessage if I activate via Redsn0w hacktivation. ( Too bad. I will choose to stay with 4.2.1 since it works fully even though a lot of programs stop supporting 4.2.1.