Bluetooth communication with smartphone, options?
Your use case sounds like a perfect match for Bluetooth LE. I would seriously consider it. The biggest disadvantage would be, as you hinted at, older smartphones don't support it. However, adoption is growing rapidly. Apple's iOS devices (iPhones, iPads, iPod Touches) support Bluetooth LE as far back as the iPhone 4S, iPad 3 &amp; iPad Mini, for example. Pretty much all recent Android devices support it too, from my understanding.

The smartphone integration of Bluetooth LE will be much easier than Bluetooth Classic (particularly on iOS, if that is relevant to your product).

There's a whole bunch of BLE chipsets and modules already available. A few suggestions: http://www.ti.com/product/cc2541, http://www.bluegiga.com/bluetooth-4.0-modules 

If you absolutely need to support legacy devices, then a dual mode Bluetooth chipset like the TI CC2560 would probably be your best bet. I don't have much experience working with legacy Bluetooth so can't offer much more in that area.