Permit me but I'm just a newbie in Java programming. I want to understand the principles and technologies involved in developing mobile apps like 2go, whatsapp etc. How they communicate with their servers and, most importantly, what the nature of those servers are? I invite your answers. Thanks in advance.

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Still waiting for responses... Can someone enlighten me, pls?

Ok dis your answer, 2go is a J2me application. Dat works on blackberry and nokia devises. Own by a south African.when u have an app of dat magnitude there are some companies in Europe or north America that can help in hosting your server for you. As for the way they monetise their app(2go) its easy . There is a company in UK that will handle that for you. They will be the one to represent you in all the country that will use your app.eg having.agreement with Mtn and co.its call in-app billing. In every money collected from the app Mtn will take 60%, the monetisation company will take 10% while you will have the remaining 30%.Mtn are greedy people it used to be 70\30. 70% for them,you 30%. your own job is just to advertise your app.as for building an app pls forget java applications to be honest don't ask me why but trust me its a dying field.concentrate more on ios ,andriod and blackberry(RIM)formats. They are the future.

Visit www.greenspek.com for a Nigerian example of java apps.
PS: Blackberry support Java.