FACEBOOK is testing a new feature that will allow users and companies to pay to send a message to a stranger.
At the moment, a Facebook user can send a message to someone else they are not "friends" with, but it does not go into the other person's main inbox. Rather, it is delivered to an "other" mail box.
Under the plans being tested by Facebook, users will be able to send messages directly to another person's inbox if they pay $1 (75c), dramatically increasing the chances the message will be read.
The move is Facebook's latest effort to monetise their service as it comes under increasing pressure to satisfy shareholders.
The company has looked at numerous methods to increase revenue in the seven months since it went public.
In October, it brought in "promoted posts", which allow a person to make their status updates more visible if they pay a small fee. The scheme has proved especially popular with small businesses dipping their toe into advertising on Facebook.
On Monday, Instagram changed its terms and conditions so that it could sell people's photos to third parties without their formal permission and no proceeds from a sale would go to the user.
That raised the prospect of advertisers using photos from Instagram, including pictures of young children.
On Wednesday, company chief executive Kevin Systrom said his firm never intended to sell pictures to advertisers, and yesterday he said the company would revert to its original terms of service.
In a blog post, Mr Systrom said that "because of the feedback we have heard from you, we are reverting this advertising section to the original version that has been in effect since we launched the service in October 2010".
The move is a notable victory for users, many of whom had taken to social networks to vent their frustration.
The pop star Pink told her 12 million followers: "I will be quitting Instagram today. What a bummer. You should all read their new rules."