It's worth remembering that Moya Messenger for Android is still around and still providing data free messaging (as well as to some websites like Wikipedia, weather, and some government sites) even when a phone user has zero airtime or data balance. You may have data but someone else may need to contact you without data so it is well worth installing.
In South Africa it is data free on MTN, Vodacom, Cell C, Telkom and in Nigeria on MTN and Airtel.
See Download #datafree
Download #datafree apps that do not use airtime or mobile data! This website does not use your mobile data.