We are quite familiar with WhatsApp, as our team already done few messaging Apps, so keeping the overall scope of work in mind, it cannot be done in US $3,000, which is yours budget on Freelancer website, as you want iPhone, Android App, WebServices & Back-end Admin Panel.
Let me know, if you are still interested & flexible in your budget, we can then finalize everything to kick started.
So, please click on the chat button to schedule a meeting time, after that I can revise our bid.
Look forward to hearing from you.
Regards,
YK
LEADconcept