Our customer has two domains with two-way trusted connection between them. On one of them they have a SharePoint farm. The problem is people pickers only find users that exist in the domain which has SharePoint installed. According to some msdn articles it should work without any additional configurations. Isn't it?
Had the same issue and logged a call with MS.
They said there is no documentation on the setup and configuration for this.
In the end we Recreated our Farm so that it was in the same domain.
Some helpful links that might help you: