With version 3 of Fongo for iOS and Android you can launch Fongo from your own application using the following URI schemes:
Launch Fongo: fongo://
Launch Fongo Dialpad with pre-filled number: fongotel://12263361437 (Replace 12263361437 with actual number)
Launch Fongo Messaging with pre-filled number: fongomsg://12263361437 (Replace 12263361437 with actual number)
Launch Fongo and place call to specified number: fongocall://12263361437 (Replace 12263361437 with actual number)
The URI's will work provided the Fongo app installed so you may want to put a check in place and direct the user to download and install Fongo from the App Store or Google Play.