Yes, that is the app I was using and found it worked great on my E71. Hopefully, someone can take an app like that and develope one for windows 7.5.
AFAIK, this app is not possible to be made on WP7 devices, and we don't yet know if it will be possible on WP8 (my guess is no, unfortunately). Microsoft doesn't really allow apps to mess with call features, such as call blocking and diverting and such, and I think it has something to do with the security of the phone (i.e. Download of an app that discretely, in the background, diverts incoming calls or makes outbound calls to premium numbers that charge you in the end. This exact scenario happened on Android - I guess it was busy making calls to premium numbers in the background or something)
You do have options though: If your carrier allows visual voicemail, you can turn that feature on to have your messages sent straight to your phone for playback.
You can also try a free service called "YouMail" that offers visual voicemail (as well as blocking specified callers (i.e. ignore the call once, they'll hear the "Number not in service" message, and I doubt they'll be calling back)). They don't have a 1st party app, but have an approved 3rd party one:
MagikMail (link is to the free, lite version. $1.99 for the full version)
There's also Google Voice, and since it's google it's not really supported very well on the windows phone platform, but a few people stepped up with visual voicemail services to use with google voice:
Store search results | Windows Phone Apps+Games Store (United States).
Both YouMail and Google Voice also let you access all of your voicemails on their respective websites (likely in addition to being on your phone when using the apps)