There's very little chance that you encounter this error on your iPhone when you try to activate but still, when you do, things can be a little bad.
If you happen to see the “Cannot activate your iPhone now” type of an error, it can mean a lot of things from Apple's servers going kaput (rare, but it does happen) to some issues with your iPhone. Say, if you are trying to activate a SIM on a locked iPhone, you're most likely not going to get it down unless the carrier you were on (previously) has allowed you to unlock that iPhone.
What we'll do is explore all the possibilities of fixing the activation errors on your iPhone and get it up and running. Before we dive head-first, let's take a look at the various errors that prevent your activation:
- Your iPhone could not be activated because the activation server is temporarily unavailable.
- The iPhone is not recognized and cannot be activated for service.
- iTunes was unable to verify your device.
(see this page for further details)
Here's How to Fix the iPhone Activation Errors:
The first time you see this error, it's better to wait. Chances are that the servers at Apple are truly busy or buggy which means the activation stuff isn't going through. You should wait for a few minutes before trying again.
I'd also go as far as to remove the SIM from the tray and then re-inserting it onto the tray and then trying to go through the activation process again.
Restarting your iPhone is going to be one of the simplest ways to try and fix the error. While it doesn't instantly guarantee that your activation will go through smoothly, there's a strong chance of that happening. You know how to restart: hold the power till the slider shows up and then slide it to turn off. And now, reboot your iPhone to try activating it again.
3. Lock/Unlock SIM Status
In case nothing works, you should probably check to see if the problem is with the SIM-card / carrier. If you are trying to activate a different carrier on a locked iPhone (which hasn't been unlocked yet), you'll get the activation errors obviously.
In these cases, you'll have to call the carrier directly and ask them to activate your iPhone+SIM card. Most of the time, the support executive will guide you through the activation process. If you have an iPhone which was on a different carrier (earlier) and now you're trying to activate a different carrier, you should know that the earlier carrier should've unlocked your iPhone.
4. Wifi / Network Issues
May be it's the Wifi/network that's causing the issue? May be your network is blocking gs.apple.com on a couple of ports. To test this, you should get connected to a different Wi-fi source than the one you are using now.
5. Via iTunes
This is where it gets a little tricky but useful. If things don't work still, you should try to activate your iPhone via iTunes. To do this, simply connect your iPhone to your computer via the USB cable. Turn it off and reboot – which triggers iTunes to open. (if it doesn't open, manually open iTunes).
Once iTunes detects your iPhone, it might ask you to go through a few steps to activate your iPhone. Although this happens less frequently as most people activate directly on their iPhone, you might be able to fix the issue.
And in case you're not able to fix it, then it's time to roll up the sleeves and restore the device.
Turn off your iPhone and then connect to your computer.
Open iTunes and then switch your iPhone on. iTunes will tell you that it has detected an iPhone and would you like to restore your device. Yeah, we do need to restore the iPhone so go through the restore process.
Once restored, try activating the iPhone again.
7. Talk/Take to Apple Care
If nothing works, may be it's time to call Apple Care and figure out a solution through the customer support guys.
Note: If you have jailbroken your iPhone previously (or tampered with it, hacked it or modified it in anyway other than permitted by Apple), chances are that is what is causing the activation error. Restoring should mostly set things right but if it doesn't, the jailbreaking/modification might also be a reason.