Getting call options such as skype/viber again My question is similar to this :

http://androidforums.com/samsung-galaxy-s2-international/473947-calling-dialer-viber-skype.html 

But not quite the same. I've chosen phone as my default calling options, and I'm ok with that. Now my question is that, what do I press when I want to call a contact via Viber/Skype/Other app again? What do I press to get asked again?

Without resetting the default calling option, is there a such option ?
The option to choose what application to use when making a call (or anything else, such as open a webpage) happens when you don't have a default set. So if you want to get asked whether to use Dialler/Skype/Viber when you try to call a contact, then you need to clear the default settings for Dialler. You won't get the prompt otherwise.

There is no way to set this up on a per-number or per-contact basis in the Dialler.