PHPT tests all work, though they take a long time to run since they do run against the live service. I wonder if PHPT format allow for mock objects, so that we could split some tests into local unit tests while still allowing for live system/integration tests like the current ones.
Code and docblocks look good.
I'd add some notes (even if marked as @internal) to the __call() docblock to highlight the usage of the "@" error suppression, so that anyone trying to troubleshoot will be advised that such suppression is occurring.
Nice compact codebase wrapper for such a wide-method service... kudos ;)