Skype will be coming to mobile devices. 

Tomorrow, Skype will be launching its free iPhone app which will allow users VoIP over WiFi networks, along with the usual messaging service Skype enables, reports the New York Times.  In May, a BlackBerry version will be released.  

Skype will abide by Apple's limitations on all voice applications for the iPhone.   Currently, Apple allows VoIP applications to make calls only when a user is within a Wi-Fi network.  This restricts users from using the carrier's data networks - quite a limitation.  If allowed, users could probably make a dent in the amount of phone calls they make by using free VoIP calls instead.

Founded in 2003, Skype currently has 405 million registered users globally.  

Skype won't be the first to offer VoIP.  Up until tomorrow, most users will have been making VoIP calls on their iPhones using applications like Nimbuzz and fring, both which allow users to use their Skype accounts within its applications.