Virtually all new cellphones as of 2015 have dual-mode chips supporting both Bluetooth classic and Bluetooth smart technologies that make them compatible with Bluetooth headsets. Most Bluetooth headsets feature a universal design that ensures compatibility with old and new cellphones.
Some older phones and headsets are not compatible. Many headset manufacturers have compatibility charts that allow the user to search for headsets that work with a specific cellphone make and model. To check compatibility of older equipment, turn both devices on and activate the Bluetooth networking on the cellphone. It scans for devices, and if the headset is compatible, it shows up in the phone's device list so it can be paired.