iPhone 6s plus ‘activation not complete’ error

When you see the “error” message try pressing the Home Button, you should get a dialogue with three options, one of which is “Start Over”. Keep trying this if necessary for several attempts, it’s been known to suddenly allow the process to continue!

Failing that you could try with another Sim card, one borrowed from a friend for example, it’s only required initially to get past the activation section after which you can put your one back in the device.

This article has a few other ideas including a Forced Restart and simply waiting a while before trying again.

http://www.irefone.com/how-to-fix-activation-error-when-ios-11-update.html

diendecay wrote:

...Is there any other Apple service that can resolve this issue with IMEI number or with something unique to the phone?

Not that I can think of, Apple's suggestions for this issue If you can't activate your iPhone - Apple Support ranges from trying another WiFi connection (a friends for example) to just keep trying (which could point to a server issue in some areas).

It might be a good idea to try another cable and again as Apple advise make sure iTunes is the latest version.

But from what I've read posted by others, "time" may be the only fix, ie. keep try at different times of the day or even the next morning.

Failing that you could always try contacting Apple Support via phone first to see if they can help remotely, other than that it may well be a Store visit. Contact - Official Apple Support

Forgot to add, if you do decide to contact Apple via phone the best way is to go to web site (link in above post) and then navigate to raise an issue (open a ticket), after filling out a few questions regarding device and problem you then should get options on how you communicate. I usually select “call back” and a time or period is usually stated, after which someone from tech should ring you.

When I’ve had to do same Apple have always called back within a few minutes and the best part is they are already aware of issue since you filled that part out at the start. It shouldn’t cost even if you are outside the guarantee because it’s more than likely a services issue which is totally under their control, but I’ve even put some issues down to new OS releases of software, again Apple appear to understand and just try and resolve, really great service and it’s why I stick with their products.