I'm also having issues with my Plantronics 925 and iPhone 4. Sound is muffled, garbled, far away, etc. Called Apple Support, and we went through a number of things, including resetting my network settings, and then re-opening WiFi and re-pairing my headset. After all that, it sounds somewhat better. Am considering ordering the Plantronics Discovery 975 and seeing if it works better (can return to Amazon if it's about the same). Apple support didn't give me any sense of "we know this is a problem and we're working on it", it was more like "it's your headset, try a different one".