I just checked the Talko's Android app , they just have 1000-5000 downloads.
Looking at the features and UI,there are far more better apps.
Then why Talko?
Cheaper than recruiting the engineers individually? I didn't see terms but if it's small, it could be a bargain to get the team and tech and roll it into Skype. Also, the better apps might not have been for sale.
Talko is a start up by Ray Ozzie.
He is one of the Microsoft Pioneer and Past Architect of Microsoft.