Android : send message (IP not SMS) using phone number

I am hunting for an android app (preferably open source) (function similar to watsapp) that allows me to send a message to a phone (using phone number) (not SMS, but just IP) even if the receiving end does not have the app installed on his phone.

Tried with TextSecure but it requires the app to be installed on both sides.

Does anyone knew if such an app exists. Kindly suggest me.