Whatsapp protocol does not actually implement ssl. It uses port 443 to transmit proxies. All data, including messages and contacts, is presented in plain text for all to see.
To sniff data:
You can create a special wireless access point on your computer (make sure that it is connected to the Internet using an Ethernet cable, otherwise you will be offline) connect to this network using ip iphone, on computer ur miss any packet sniffer (I personally use wirehark) and the tcp port 443. viola filter, you will receive both requests and a response from whatsapp servers without intercepting data.
To intercept data:
I never did , but I think you can just use the iPhone settings (settings-> general-> network-> vpn-> add vpn configuration-> proxy settings (manual)) for the proxy server of all the network under port 443 on the server that you have, you will need to run a proprietary program that processes requests and sends them (processed) to whatsapp servers.
About data:
From what I remember, some data inside the protocol is encoded (substitutions / base64 / other basic encodings).
About your question regarding proxy transmission. Hope my answer on how to smell will solve your problem.
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