Mobile phone users in Africa are being encouraged to send text messages in support of a women's rights petition.
Africa has many more mobile phone users than e-mail users
Campaign groups are pressing leaders to ratify the African Union (AU) Protocol on the Rights of Women.
Oxfam and human rights group Fahamu are among the organisations behind the online petition.
A year after being adopted by the AU, just three countries have ratified the protocol. At least 15 signatures are needed for it become legally binding.
Comoros, Libya and Rwanda have given their backing to the protocol, which is designed to guarantee women's rights to health, education and justice, as well as protection against violence.
The coalition of human rights groups, which also includes Equality Now, Credo and Femnet, say their online campaign is designed to put pressure on African governments.
Africa has considerably more mobile phone users than e-mail users.
By targeting them, the campaign groups hope to boost support for their online petition.
Those wishing to SMS their support for the Protocol on the Rights of Women in Africa can do so by sending a text message or SMS to +27-832-933934, with the word "petition" and their name in the message.
Text number: +27-832-933934
Send the word "petition" and your name
You will be charged the cost set by your network for sending an international SMS
Senders will be charged the cost set by their network for sending an international SMS.
Firoze Manji, Director of Fahamu, said: "To our knowledge, this is the first time that SMS technologies will have been used on a mass scale on the African continent in support of human rights."
"The facility enables those with poor or non-existent internet access to sign the online petition and takes advantage of the fact that there are about eight times more mobile phone users compared to e-mail users in Africa."
It is estimated that there are currently 52 million mobile phone users in Africa. The continent is set to reach 67 million mobile phone users by the end of the year.