Internet telephony firm Skype made its first major leap into cellphones on Tuesday, striking a deal with the largest US mobile carrier Verizon Wireless.

Skype's free calls on computers have become an Internet phenomenon since the company was founded in 2002, and it has some 520 million registered users around the globe.

So far it has found little traction on wireless - with only British operator 3 embracing it - as most telecoms operators have seen it as a risk to their core business of voice calls.

"Verizon and Skype getting together is like Tom and Jerry making peace," said one senior telecoms industry executive, who wished not to be named. While operators such as AT&T Inc tolerate customers using Skype applications on cellphones, Verizon is the first US operator to actively push the service, which will work on phones such as Research In Motion's BlackBerry.

"This is a breakthrough," Skype chief executive officer Josh Silverman said in an interview.

"We sense a real shift in operators thinking. Some operators attitude is rapidly changing," Mr Silverman said.