I may well be the last person to find out about this device....it's been on the market for quite a while now, but hopefully this video will still be of use to someone. I demonstrated this in the video with an iPhone, but it should work fine with any devices that can output their audio via bluetooth.
I don't own a decent Android phone, so I'm not familiar with how voice control operates on them, but if it can be activated by a press of the 'answer' button on a bluetooth headset, then it will work fine. This device can perform every function you can activate by pressing an answer button on a normal bluetooth headset
If you shop around you can usually get this at a good discount. At the time of writing, it's on Amazon for £40.99