Phone Not allowed only on three network

How long it takes may depend on whether they agree to do so at all. The only reasons to blacklist it under normal circumstances are because it was reported lost or stolen or the account holder who was using it reneged on their contractual obligations, didn't pay their bill or termination fee, etc. I'd imagine the seller is going to have to cough up some cash to get this resolved.

You may just want to consider returning it and getting your money back.

Blacklisting varies a great deal country to country. In some, individual carriers may blacklist, but not share black listings with other carriers.

The USA has a universal carrier blacklisting, and Canadian carriers and most or all Mexican carriers participate in that. But most countries do not have any mandated universal cell phone blacklisting.

So all you can do is call three and ask them about it.

Since this is a carrier issue, you need to speak with three to get this resolved.

The previous owner is going to have to request that the iPhone be unlocked from Three.

If it’s been blacklisted on three there is nothing you can do. That most likely means it was reported stolen to the carrier.

That's what I do. He bought a phone he can't use presently. I'd get my money back and buy one I could use.

Sorry, I have no idea. Three should be able to tell him or you at least roughly how long it takes them to process such a request. Since it’s a single specific carrier blacklisting, only they would know.

In the USA my understanding is it is a fairly involved process to convince a carrier a blacklisting was made in error and get them to reverse it. Which makes some sense as if it is to prevent theft by eliminating re-use of devices, then it shouldn’t be easy to remove a listing once made. But then we have an effectively government mandated universal blacklist, not a carrier specific or ad-hoc system. An individual carrier system may be able to move a bit faster to effect changes.

Anything's possible. Only three can tell you though.

Again, only three can answer that question.