O2 is to trial a Voice over IP (VoIP) service that will allow its customers to make calls over Wi-Fi networks from their smartphones.

O2 Connect, which will go head-to-head with other VoIP service such as Skype, will initially be available on Apple iPhones and smartphones running Google Android and will see calls and texts routed over the internet but still being assigned to the user's existing mobile number.

The trial will be limited to 1,000 participants who will be invited by the mobile operator to take part. If the trial proves successful it will be then be rolled out as a commercial service during 2012. O2 said if the service is made available to all its customers, some parts of O2 connect will be available free, while others will be chargeable, although it did not specify which.

"This trial will allow us to explore the potential of delivering VoIP services to customers. We hope to launch O2 Connect as a commercial service in 2012." explained Richard Porter, head of consumer mobile products, O2 in the UK.

The mobile network said the technology is the latest development from O2 Labs, which handles the introduction and beta testing with the involvement of O2 customers of new services.

O2 recently unveiled an MMS service that allows its customers to post pictures to micro-blogging service Twitter straight from their mobile phone.

Customers of the network simply need to log-in to the micro-blogging service and link their mobile phone number to their profile. Then they can compose an MMS featuring the image and send it to 86444.