From the point of UI / UX, I cannot think of a worse software than Skype (all platforms including Android).
It's always a hard struggle, effort and suffering to make a call to a phone number, even if this phone number is in the contacts of the phone, or has been called before.
Adding to that, when Microsoft acquired Skype, they were offering to merge the Skype and Live accounts, which I agreed to, which rendered my Skype account unusable (with credit on it and lot of contacts registered).
