This app was mentioned in 6 comments, with an average of 1.00 upvote
I think your tittle is misleading, whatsapp won't let to send free sms. Whatsapp only send instant messages but not free sms. I you want to send free sms you need the app https://play.google.com/store/apps/details?id=com.twin
Nice idea, but I think you can send a personal video with an app, or an audio gift, it's better I use the app twin because I can send one emoticon with sound, the birthday emotisound https://play.google.com/store/apps/details?id=com.twin
I use twin messenger because it has emoticons with sound (emotisounds) and you have chat in group with IM and free sms, all in one app.
I use the app twin messenger to send free sms and instant messages, all in one, and voice messages, chat in group, etc... did you ask that?
Yo can use to send free sms the app twin messenger
You have the app Twin Messenger to send instant messages and free sms, all in one... https://play.google.com/store/apps/details?id=com.twin