Microsoft might argue that "Teams" is not a "multi-line telephone system". That probably wouldn't go far with a jury. The clear intent of the law is that if you interpose something between a phone handset and the 911 network, it has to pass through 911 calls.
Google may blame Microsoft but there is no way an app should be able to disable 911 calling on a phone. This means that other apps could disable 911 intentionally. This is Google's problem to fix. A phone OS needs to guarantee certain things and 911 is one of them.