Currently Windows Phone 7 has a total of eight devices and only four wanders are making these devices but don’t think these are the only companies which will make Windows Phone 7 devices as many other companies will join in for WP7 devices soon.And as Sony Ericsson is one of the names partner for Windows Phone 7 so their device may come soon this year. 
So , Sony Ericsson may have not shown any of their device till now but recently a picture of Sony Ericsson Windows Phone 7 device has leaked in the wild.This leaked image is shared by Lizhecomb and it looks like a working prototype of Sony Ericsson WP7 device which may launch soon.
If this prototype is real and if is supposed to launch soon then with this device and if we also add Asus WP7 device then it would give the users Windows Phone 7 a waste choice of handsets just like the Android users.