Can't get past the activation screen for iphone 3Gs

Where exactly did you get the phone? Where are you, and what carrier are you trying to use?

I ask because this is often symptomatic of a phone that was jailbroken or hacked at some point to unlock it.

Is your friend also on Telus or on a different phone carrier? If he/she isn't on Telus, tell them to have the phone unlocked for you so you can use it with Telus.

Had your friend jailbroken the phone? Had your friend gotten the phone second hand and "unlocked" it so they could use it with Telus?

Call AppleCare and give them the serial number of the phone. Ask them what carrier it is locked to.

I'll lay odds the phone was either jailbroken or hacked to unlock it to begin with. If that's the case, and you gave your friend actual money for the phone, tell them you want your money back. It's a brick.

Have you tried activating it over 3G instead of WiFi? If there is a problem on your network that's preventing the phone from communicating with the activation servers, it stands to reason that the problem would affect your computer as well (assuming the WiFi you're attempting to use to activate and the computer are on the same LAN).

Jailbreaking the phone won't do any good at all. It will void any remaining warranty and forfeit your right to support from Apple and on these forums.

You might want to take the phone into Telus and see if they can help you. You may just need a replacement SIM.

Anyone had this issue resolved without jailbreaking/unlocking.

I have an iphone 3gs with AT&T that I bought from a guy 3 years ago and used till Dec 2012 with OS 4.x.x. I never used it untill last week after upgrading to latest OS 6.1.3. It never worked since then and stuck at "activation server is unavailable and to try again .. " Called AT&T to verified the IMEI is in good standing. I tried activating using itunes store with no luck as well. Went to AT&T store and checked with other SIM cards with no luck and asking me to contact Apple.

You are asking in a thread that is 18 months old. Whatever.

Here are possible causes for that message:

1. Your antivirus is blocking access to gs.apple.com.

2. Your phone is jailbroken.

3. Your computer has been used at some time in the past to jaibreak some iOS device (not necessarily the phone with the problem), and its network database was corrupted by the hacking software that was used.

4. Apple's activation servers are down (very rare, and never for more than an hour or so).

For 1. try disabling your antivirus.

For 2. & 3. you need to go somewhere other than an apple forum for help. Although you can try deleting lines containing gs.apple.com from your "hosts" file on your computer.

Windows: c:\windows\system32\drivers\etc\hosts

Mac: /etc/hosts

"activation server is unavailable" error is displayed only when I try to activate the phone via WIFI/data plan.

Using itunes it says "sim is not valid". But the same sim works with my android smartphones without any issues.

Antivirus could not be blocking access to gs.apple.com it since I restore the phone/reinstall the OS couple of times without any issue using itunes. Doesn't it connect to Apple to verify the OS?

SIM is not valid means that the phone is locked to a carrier different from the carrier the SIM is for.

Its an AT&T phone and AT&T sim card - same phone and carrier

Then it's possible it's failing. If you've tried restoring it as a new device, and it won't recognize an AT&T SIM that works in another iPhone, about the only thing left to try is a DFU mode restore. If that still doesn't fix it, it's time to either get it replaced or trade it in for something a little bit newer.