The VOIP software firm Skype has reached an agreement with US telecoms firm Motorola that should help it to increase its penetration of the wireless market.

The Luxembourg company plans to load Skype software onto some Motorola Wi-Fi or third-generation mobile phones in the future. This would enable mobile subscribers to make free national calls and cheap international calls by using the internet to carry calls, rather than standard mobile networks.

Motorola and Skype will first of all co-market products such as Bluetooth, or wireless, equipment, before introducing handsets with pre-installed software.

Skype's software, which needs to be used with a high-speed internet connection, enables users to make free phone calls over the internet. It has already attracted 26 million registered users since it was launched 18 months ago.

It said this week it was currently attracting 140,000 new registered users per day.

Many analysts believe that in the future mobile handsets will use a variety of ways to connect to the internet, including third generation mobile, Wi-Fi and WiMAX technology. This will make it more difficult for the mobile network operators, such as Vodafone and O2, to charge for basic mobile phone calls.

Skype, which is the most successful VOIP software firm in Europe, completed its last fund-raising more than a year ago. It said this week that it would not need more cash in the near future, and was not planning an initial public offering.

Additional reporting: Reuters