Here is the current situation as I understand it.
1. Android phones: once Android supports BT-Smart and apps are updated to support BT-Smart senors (or more correctly, device profiles), then it will work.
2. Windows phones: From
Nokia's site,
At time of writing (31st October 2013) no public APIs are available for accessing features of Bluetooth 4.0 LE on any device.
Underlying support (without public APIs) for Bluetooth 4.0 LE is enabled on Nokia Lumia 520, 620 & 720 by the Nokia Lumia "Amber" update. All other Nokia Lumia WP8 smartphones are expected to receive BT LE support as a future software update.
So, one has to wait for the release of public API's for developers to write apps. At that point, Windows phones can be used as bike computers with supported sensors.