I want to find a way so that people browsing a website from a smart phone can contact the company via any of the preferred methods.
Doing it for Skype is easy... but what about Viber/Whatsapp/iMessages/FaceTime?
Is that possible?
It's possible.
You have to know url scheme which this apps registered for themselves. Of cause, if they did it.
For example Facebook application uses fb://
scheme. For other applications look through their ipa files (main plist files)