iPhone 3GS on iOS 4 with AT&T unlimited data plan, experiencing loss of data?

Just heard from one of the folks we know who updated his iPhone 3GS to iOS 4 yesterday only to lose his AT&T data connection completely. Today, when he could no longer even place calls, he contacted AT&T who, after several escalations, informed him there are isolated incidents of iPhone 3GS on iOS 4 with unlimited data plans no longer being able to connect to the network.
They told him they're working with Apple to fix it, and put him name on a contact list so they could let him know when it was resolved.
Our question is -- how isolated is isolated? How's your AT&T unlimited data post iOS 4 update?
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Rene Ritchie is one of the most respected Apple analysts in the business, reaching a combined audience of over 40 million readers a month. His YouTube channel, Vector, has over 90 thousand subscribers and 14 million views and his podcasts, including Debug, have been downloaded over 20 million times. He also regularly co-hosts MacBreak Weekly for the TWiT network and co-hosted CES Live! and Talk Mobile. Based in Montreal, Rene is a former director of product marketing, web developer, and graphic designer. He's authored several books and appeared on numerous television and radio segments to discuss Apple and the technology industry. When not working, he likes to cook, grapple, and spend time with his friends and family.