Q: how i can activate my second-hand iphone 4s without referring back to old owner ? I purchase it from second-hand shop ; i have purchasing invoice

If you mean the device is in 'Activation Lock', which means that you need to input an Apple ID & Password to get past taht screen during the Setup Assistant, then there is no method available.  You need to contact the point of sale, and ask them to remove the Activation Lock, or refund your money.

If you cannot get the shop to make contact with the former owner to have Find My iPhone removed, then you will NEVER be able to activate the phone. It is useless to you, and in your words yes, a piece of steel.

Zeyad1974 wrote:

money is not refundable 

Then you're the proud owner of a paperweight. Next time, purchase from an official source.

Your phone is activation locked. This is an anti-theft feature of the iPhone. That means that the previous owner did not give up possession of it; this also most lkely means the phone was stolen. It is useless to you; you will never be able to make it work. The store that sold it to you should not have sold a non-working phone to you. If they will not take it back go to the police, as they are most likely a dealer in stolen phones.

"That means that the previous owner did not give up possession of it; this also most lkely means the phone was stolen."

No, it does not "mean this".

It simply means the previous owner did not turn off findmyiphone.

The number of people who forget to turn off Find my iPhone before selling the phone I suspect is vanishingly small, because erasing the phone (which any sane person will do before giving away or selling a device that is full of personal information) requires turning off Find my iPhone and thus Activation Lock. Thus, I stand by my statement that it most likely means the phone was stolen. Not a guarantee, but it's a good place to put your bet.

Your phone is activation locked. This is an anti-theft feature of the iPhone. That simply means that the previous owner did not turn off FindMyiPhone. Thats all it means. Nothing else.

If you do not have the previous owners contact info or their AppleID/password, you will not be able to use the iPhone.

You should take it back & get a refund.

Lawrence Finch wrote:

 

because erasing the phone (which any sane person will do before giving away or selling a device that is full of personal information)

Yeah, you'd think people would do this, would you?

Many people don't (so they must be insane?), they simply delete stuff and some don't even do that.

and this must be only the insane people or thieves out there, right?