WhatsApp - writing a clone (iphone, android, wp7)

Question

I am trying to create a instant messaging app very much like whatsapp I suppose. My resources I have available to me are Server development in C# (REST Service, dedicated server app etc)

And currently an android development platform using eclipse (iphone, wp7 to follow later). I have done some development in Android before but I don't have any idea where to start an application like this.

My guess would be it would work with UDP / TCP or similar ? I currently have a shared server for an asp.net website but I presume this wouldn't be ideal, I could essential setup a web service on the server and get a client to publish his messages there but then this would mean that the receivers would have to POLL (PULL) every 5 minutes or so - so I guess this wouldn't be real time

Do I need to use UDP here ?

And I presume platforms like Iphone, Android and WP7 will not have any issues sending msgs by UDP - if that is how its done.

I look forward to any help or guidance.

Solution

As all the other comments already suggested you should go with XMPP - there is a huge collection of available libraries you can find here.

Best wishes, Tim