The "industrial" design of the iPhone 4, introduced in mid-2010, was a favorite -- especially considering that the same design was replicated not only in the following year's iPhone 4s but (in larger-screen form) in the successor iPhone 5, iPhone 5s, and iPhone SE. But it wasn't without its problems, specifically those involving (quoting Wikipedia) its "uninsulated stainless-steel frame which doubles as an antenna".
As GSM cellular carrier-base customers quickly learned, its received signal strength could vary widely depending on how it was held (assuming an insulating "bumper" or other case wasn't on it) and how the results were reported. And then-CEO Steve Jobs' initial response to the reports ("Just avoid holding in it that way") wasn't exactly helpful either. The antenna was redesigned in time for the CDMA-friendly version of the handset, which appeared eight months later, along with the follow-on GSM-plus-CDMA model in mid-2011.
To be clear, the iPhone 4 ended up selling quite well, anyway. Wikipedia notes that it "had the longest lifespan of any iPhone ever produced, spanning close to four years and available in some developing countries until early 2014. But those first few months were pretty rocky, and one can only guess how much better the iPhone 4 might have performed in the market absent Antennagate.
(Image source: By Justin14 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)