I wouldn't doubt Apple is working on a deal with a carrier in China, but I don't think you'll see one any time soon. There are 70+ countries that have already signed the deals, and Apple has only caught up to the first 25. Demand worldwide is exceptionally high, and being able to keep up with China might not be possible until the demand goes down.
I would follow the above post and get your client a legitimate phone they can use from outside the country, assuming you are able to do that.