RIM has entered Skype territory after unveiling an Internet voice chat function for its BBM instant messenger.

BBM Voice works over WiFi connection and only works if both users have a BlackBerry phone. The feature comes with the latest update of the service.

RIM hopes the feature will allow the BlackBerry to remain relevant at a time when Microsoft's Skype and Google's Talk change the way people communicate over mobile technology.

Users can switch between BBM Voice and BBM text chat to talk and a split-screen feature allows customers to talk and text at the same time.

However, BBM Voice still lacks the video chat functionality and 3G support found in Apple's Facetime, Microsoft's Skype and Google+ Hangouts.

Both Microsoft's and Google's products can also work on platforms apart from their own Windows Phone and Android-based operating systems.

"BBM is the quick, easy way to stay connected to the people that matter to you, and with today's announcement we're expanding the capabilities of the service for deeper social engagement and even greater collaboration, beginning with voice functionality," said T.A. McCann, Vice President of BBM and Social Communities at RIM. "The new BBM Voice feature is for when you're travelling and you want to call home without worrying about phone charges. It's for when you have news you can't wait to share, for quickly explaining complicated details, and collaborating with colleagues. Whenever your ideas are too big for text, there's BBM Voice."

News of BBM Voice comes ahead of the much-delayed release of the Blackberry 10 operating system in January.

RIM is hoping that its new OS will help reinvent the business as it faces declining revenue. Once a leader in the smartphone sector, the Canadian firm has suffered in the face of competition from Apple and devices using Google's Android.

However, the company hopes to revive its fortunes with a particular focus on developing markets. It said that its new BBM Voice feature will be particularly attractive to those regions because it offers a cheaper alternative to SMS text messaging.

The new feature currently only works on Blackberry 6 and 7 smartphones, but RIM plans to expand this to include Blackberry 5 devices as well.