Apple has posted about some consequences of jailbreaking your iPhone but I experience one of the “consequences” daily on a stock iPhone:
Unreliable voice and data: Dropped calls, slow or unreliable data connections, and delayed or inaccurate location data.
So maybe the tech support article should have been titled “Unauthorized modification of iPhone OS (or using AT&T) has been a major source of instability, disruption of services, and other issues”