untangle-dangle
What you periodically hafta do with your handset's curly-cord to get da knots outta it --- when it gets snarled up enough, simply tugging on it just doesn't do da trick anymore... ya gotta actually unplug da cord at both ends, carefully unravel da kinks, and then suspend da cord from one end so that it can hang freely to allow it to "naturally" untwist and "equalize" itself.
Adding a swivel-adapter to your handset-cord can indeed sometimes help to reduce its getting all wrapped up around itself and save your having to perform da untangle-dangle so often, but da problem with these doodads is dat dey tend to not have very good swivel-contacts, and so you soon get a lot of static and intermittent sound. Plus da cheaper units tend to not swivel very easily, and so you gotta keep spraying them wif WD-40 to keep them twisting around freely.