As you might know, Bluetooth Low Energy (or Smart) is the core technology used for iBeacon and Eddystone, so it’s critical that as many phones as possible support BLE, for a broad deployment. If a phone says it supports Bluetooth 4.0, it supports both traditional Bluetooth and BLE.
The Bluetooth SIG keeps a list of such devices, and it has become long lately: Bluetooth SIG – Bluetooth Smart Ready products
Of course, Bluetooth needs to be turned on as well, so advise users/customers about this.