For an updated discussion, read this recent comparison between SMS and Voice for data gathering in Indonesia.

We live and work in the Philippines, which has been dubbed the “Text messaging capital of the world.” So we are very familiar with the power of 160 characters.

But as a social enterprise whose goal is to eliminate poverty, we are familiar with another thing: the fact that globally, 11.4% of men and a shocking 20.1% of women are illiterate. They cannot read or write.

They cannot text.

Of course, rates of illiteracy are even higher among the most vulnerable populations: the poor, women, and the elderly. The regions of highest illiteracy are South and West Asia (adult illiteracy rate 37%) and Sub-Saharan Africa (adult illiteracy rate 61%). In eleven countries, over 50% of the adult population is illiterate.

At engageSPARK, we believe SMS and Voice are both powerful tools for change. That’s why we easily allow you to build and launch an SMS or Voice engagement in just minutes. But how do you know which to use?

You might want to use voice if:

• You know your beneficiaries have low levels of literacy, or if they are in a highly vulnerable population group such as women or the elderly, who tend to be less literate.
• You are sending messages in a country whose technology infrastructure doesn’t support texting in all local languages. In Cambodia, although there are more mobile phone subscriptions than citizens, most basic phones that poor people have access to cannot display text in Khmer, the only language most of the population can read and write. engageSPARK can send messages in any local language with Unicode, but can the recipient’s phone can receive it?
• You want your recipients to respond to a survey. During a voice survey, all recipients need to do is press one key to respond. It’s simple, easy, and free for the recipient. engageSPARK has seen response rates up to 50x higher for voice polls vs. SMS polls.
• You have an already established relationship with the people you will be messaging. With engageSPARK, you can send a voice message of your own pre-recorded voice, which can instantly establish trust among recipients.
• You want to persuade listeners via the tone of your voice, use an engaging story, or have a lot of information that you want to convey. Here is a great example of in-the-field health workers receiving training via voice messages, saving time and money because they didn’t even have to leave work for the training!
• You want a lot of good data that you can use for reporting to managers and donors. With voice messages, engageSPARK can show you detailed information including whether a call was answered and how long it was listened to, which simply isn’t available with SMS.

You might want to use SMS Text messages if:

• You know that your beneficiaries can read the language you are sending (and write, if you are expecting a response).
• You know that the phones you will be sending messages to can receive and properly display messages in the local language.
• You want to send a message very quickly. SMS allows you to be short, sweet, and to the point. Plus, 90% are read within three minutes.
• The message needs to be saved and viewed again later, such as the market-price of crops or the date and time of an event. (A voice option for this need exists: simply give the recipient a number to send a “missed call” to, sometimes called flashing or beeping. After the missed call, which is free, engageSPARK can call the person back immediately and replay the message).
• If the message is purely for educational or informational purposes, and it is not of high importance whether or not you receive a response (we found voice surveys had a dramatically higher response rate than SMS surveys).
• You want to send messages to improve literacy. For semi-literate populations, this could be done via only SMS. For illiterate populations, you could combine text with voice. Check out this amazing project that used SMS to increase English literacy rates by 50% in Papua New Guinea!

Want to read about a specific case? Unilever recently made efforts to test both SMS and Voice for data collection—find out who the winner is here.