You can't. Smartphones are Class 2 devices (weak), and you must use radio the way firmware let's you.
Purpose-built hardware is Class 1 (much stronger, 100 mW/20dBm vs 2.4mW/4dBm), and they can use sophisticated protocols to keep the connection stable. And that's Bluetooth.
If they're not playing Bluetooth but go general ISM, they can emit whole 1W on 2.4GHz or 915 MHz.
Purpose-built hardware is Class 1 (much stronger, 100 mW/20dBm vs 2.4mW/4dBm), and they can use sophisticated protocols to keep the connection stable. And that's Bluetooth.
If they're not playing Bluetooth but go general ISM, they can emit whole 1W on 2.4GHz or 915 MHz.
They're not really alike.