The service allows Facebook users to buy credit and send text and picture messages from their PC to any mobile phone.
Mobile users who receive Facebook texts can reply directly to the Facebook profile of the person who sent the text.
Anyone who installs the Vodafone Connect to Friends Facebook application gets 25 free text credits to trial the service.
Once the free credit is used up, more credit can be bought using PayForIt WAP, with texts costing 10p each and MMS at 30p each.
Pieter Knook, director of internet services at Vodafone, said the service offers a ground breaking social networking opportunity.
He added that with 20 million UK users of social networking sites, it is the perfect time to trial a texting via Facebook service.